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openvpn(8)							    openvpn(8)

       openvpn - secure	IP tunnel daemon.

       openvpn [ options ... ]

       OpenVPN	is  an open source VPN daemon by James Yonan.  Because OpenVPN
       tries to	be a universal VPN tool	offering a great deal of  flexibility,
       there are a lot of options on this manual page.	If you're new to Open-
       VPN, you	might want to skip ahead to the	 examples  section  where  you
       will  see how to	construct simple VPNs on the command line without even
       needing a configuration file.

       Also note that there's more documentation and examples on  the  OpenVPN
       web site:

       And  if you would like to see a shorter version of this manual, see the
       openvpn usage message which can be obtained by running openvpn  without
       any parameters.

       OpenVPN	is  a robust and highly	flexible VPN daemon.  OpenVPN supports
       SSL/TLS security,  ethernet  bridging,  TCP  or	UDP  tunnel  transport
       through	proxies	 or  NAT,  support  for	dynamic	IP addresses and DHCP,
       scalability to hundreds or thousands of users, and portability to  most
       major OS	platforms.

       OpenVPN	is  tightly  bound to the OpenSSL library, and derives much of
       its crypto capabilities from it.

       OpenVPN supports	conventional encryption	using a	pre-shared secret  key
       (Static	Key mode) or public key	security (SSL/TLS mode)	using client &
       server certificates.  OpenVPN also supports non-encrypted TCP/UDP  tun-

       OpenVPN	is designed to work with the TUN/TAP virtual networking	inter-
       face that exists	on most	platforms.

       Overall,	OpenVPN	aims to	offer many of the key features	of  IPSec  but
       with a relatively lightweight footprint.

       OpenVPN allows any option to be placed either on	the command line or in
       a configuration file.  Though all command line options are preceded  by
       a double-leading-dash ("--"), this prefix can be	removed	when an	option
       is placed in a configuration file.

       --help Show options.

       --config	file
	      Load additional config options from file where each line	corre-
	      sponds  to  one  command	line option, but with the leading '--'

	      If --config file is the only option to the openvpn command,  the
	      --config can be removed, and the command can be given as openvpn

	      Note that	configuration files can	 be  nested  to	 a  reasonable

	      Double  quotation	or single quotation characters ("", '')	can be
	      used to enclose single parameters	containing whitespace, and "#"
	      or ";" characters	in the first column can	be used	to denote com-

	      Note that	OpenVPN	2.0 and	higher performs	backslash-based	 shell
	      escaping for characters not in single quotations,	so the follow-
	      ing mappings should be observed:

		  \\	   Maps	to a single backslash character	(\).
		  \"	   Pass	a literal doublequote character	("), don't
			   interpret it	as enclosing a parameter.
		  \[SPACE] Pass	a literal space	or tab character, don't
			   interpret it	as a parameter delimiter.

	      For example on Windows,  use  double  backslashes	 to  represent

		  secret "c:\\OpenVPN\\secret.key"

	      For   examples   of   configuration   files,   see  http://open-

	      Here is an example configuration file:

		  # Sample OpenVPN configuration file for
		  # using a pre-shared static key.
		  # '#'	or ';' may be used to delimit comments.

		  # Use	a dynamic tun device.
		  dev tun

		  # Our	remote peer
		  remote mypeer.mydomain

		  # is	our local VPN endpoint
		  # is	our remote VPN endpoint

		  # Our	pre-shared static key
		  secret static.key

   Tunnel Options:
       --mode m
	      Set OpenVPN major	mode.  By default, OpenVPN runs	 in  point-to-
	      point   mode   ("p2p").	OpenVPN	 2.0  introduces  a  new  mode
	      ("server") which implements a multi-client server	capability.

       --local host
	      Local host name or IP address for	bind.  If  specified,  OpenVPN
	      will  bind  to  this address only.  If unspecified, OpenVPN will
	      bind to all interfaces.

       --remote	host [port] [proto]
	      Remote host  name	 or  IP	 address.   On	the  client,  multiple
	      --remote options may be specified	for redundancy,	each referring
	      to a different OpenVPN  server.	Specifying  multiple  --remote
	      options  for  this purpose is a special case of the more general
	      connection-profile feature.  See the <connection>	 documentation

	      The  OpenVPN client will try to connect to a server at host:port
	      in the order specified by	the list of --remote options.

	      proto indicates the protocol to use  when	 connecting  with  the
	      remote, and may be "tcp" or "udp".

	      The  client  will	 move  on to the next host in the list,	in the
	      event of connection failure.  Note that at any given  time,  the
	      OpenVPN client will at most be connected to one server.

	      Note  that  since	 UDP  is connectionless, connection failure is
	      defined by the --ping and	--ping-restart options.

	      Note the following corner	case:  If you  use  multiple  --remote
	      options, AND you are dropping root privileges on the client with
	      --user and/or --group, AND the client is running	a  non-Windows
	      OS,  if  the  client  needs to switch to a different server, and
	      that server pushes back different	TUN/TAP	or route settings, the
	      client may lack the necessary privileges to close	and reopen the
	      TUN/TAP interface.  This could cause the client to exit  with  a
	      fatal error.

	      If --remote is unspecified, OpenVPN will listen for packets from
	      any IP address, but will not act on those	 packets  unless  they
	      pass all authentication tests.  This requirement for authentica-
	      tion is binding on all potential peers, even  those  from	 known
	      and  supposedly trusted IP addresses (it is very easy to forge a
	      source IP	address	on a UDP packet).

	      When used	in TCP mode, --remote will act as a filter,  rejecting
	      connections from any host	which does not match host.

	      If  host	is a DNS name which resolves to	multiple IP addresses,
	      the first	address	returned by the	system getaddrinfo()  function
	      will  be used (no	DNS randomization inside OpenVPN 2.3.x,	and it
	      will not try multiple addresses).

	      Prepend a	random string (6 bytes,	12 hex characters) to hostname
	      to  prevent  DNS	caching.   For example,	"" would be
	      modified to "<random-chars>".

	      Define a client connection profile.  Client connection  profiles
	      are  groups of OpenVPN options that describe how to connect to a
	      given OpenVPN server.  Client connection profiles	are  specified
	      within an	OpenVPN	configuration file, and	each profile is	brack-
	      eted by <connection> and </connection>.

	      An OpenVPN client	will try each connection profile  sequentially
	      until it achieves	a successful connection.

	      --remote-random  can be used to initially	"scramble" the connec-
	      tion list.

	      Here is an example of connection profile usage:

		  dev tun

		  remote 1194 udp

		  remote 443 tcp

		  remote 443 tcp
		  http-proxy 8080

		  remote 443 tcp
		  http-proxy 8080

		  pkcs12 client.p12
		  ns-cert-type server
		  verb 3

	      First we try to connect to a server at	 using
	      UDP.   If	that fails, we then try	to connect to
	      using TCP.  If that also fails, then try connecting  through  an
	      HTTP  proxy  at	to using TCP.
	      Finally, try to connect through the same proxy to	 a  server  at using TCP.

	      The  following  OpenVPN options may be used inside of a <connec-
	      tion> block:

	      bind,   connect-retry,	connect-retry-max,    connect-timeout,
	      explicit-exit-notify,  float,  fragment, http-proxy, http-proxy-
	      option, http-proxy-retry,	http-proxy-timeout,  link-mtu,	local,
	      lport,  mssfix,  mtu-disc,  nobind,  port, proto,	remote,	rport,
	      socks-proxy, socks-proxy-retry, tun-mtu and tun-mtu-extra.

	      A	defaulting mechanism exists for	specifying options to apply to
	      all  <connection>	 profiles.   If	any of the above options (with
	      the exception of remote  )  appear  outside  of  a  <connection>
	      block,  but  in a	configuration file which has one or more <con-
	      nection> blocks, the option setting will be used	as  a  default
	      for  <connection>	 blocks	 which	follow it in the configuration

	      For example, suppose the nobind option were placed in the	sample
	      configuration  file  above, near the top of the file, before the
	      first <connection> block.	 The effect would be as	if nobind were
	      declared in all <connection> blocks below	it.

       --proto-force p
	      When  iterating  through connection profiles, only consider pro-
	      files using protocol p ('tcp'|'udp').

	      When multiple --remote address/ports are specified, or  if  con-
	      nection  profiles	 are being used, initially randomize the order
	      of the list as a kind of basic load-balancing measure.

       --proto p
	      Use protocol p for communicating with remote  host.   p  can  be
	      udp, tcp-client, or tcp-server.

	      The default protocol is udp when --proto is not specified.

	      For  UDP	operation,  --proto  udp  should  be specified on both

	      For TCP operation, one peer must use --proto tcp-server and  the
	      other  must  use	--proto	 tcp-client.  A	peer started with tcp-
	      server will wait indefinitely for	 an  incoming  connection.   A
	      peer  started  with  tcp-client  will attempt to connect,	and if
	      that fails, will sleep for 5 seconds (adjustable via the	--con-
	      nect-retry  option)  and	try  again infinite or up to N retries
	      (adjustable  via	the  --connect-retry-max  option).   Both  TCP
	      client  and  server  will	 simulate  a SIGUSR1 restart signal if
	      either side resets the connection.

	      OpenVPN is designed to operate optimally over UDP, but TCP capa-
	      bility  is provided for situations where UDP cannot be used.  In
	      comparison with UDP, TCP will usually be somewhat	less efficient
	      and less robust when used	over unreliable	or congested networks.

	      This article outlines some of problems with  tunneling  IP  over

	      There  are certain cases,	however, where using TCP may be	advan-
	      tageous from a security and robustness perspective, such as tun-
	      neling  non-IP  or application-level UDP protocols, or tunneling
	      protocols	which don't possess a built-in reliability layer.

       --connect-retry n
	      For --proto tcp-client, take n as	the number of seconds to  wait
	      between connection retries (default=5).

       --connect-timeout n
	      For  --proto  tcp-client,	 set  connection  timeout to n seconds

       --connect-retry-max n
	      For --proto tcp-client, take n as	the number of retries of  con-
	      nection attempt (default=infinite).

	      Show  sensed  HTTP or SOCKS proxy	settings. Currently, only Win-
	      dows clients support this	option.

       --http-proxy server port	[authfile|'auto'|'auto-nct'] [auth-method]
	      Connect to remote	host through an	HTTP proxy at  address	server
	      and port port.  If HTTP Proxy-Authenticate is required, authfile
	      is a file	containing a username and  password  on	 2  lines,  or
	      "stdin" to prompt	from console.

	      auth-method should be one	of "none", "basic", or "ntlm".

	      HTTP  Digest  authentication  is supported as well, but only via
	      the auto or auto-nct flags (below).

	      The auto flag causes  OpenVPN  to	 automatically	determine  the
	      auth-method  and	query  stdin  or  the management interface for
	      username/password	credentials, if	required.  This	flag exists on
	      OpenVPN 2.1 or higher.

	      The  auto-nct  flag  (no	clear-text  auth) instructs OpenVPN to
	      automatically determine the authentication method, but to	reject
	      weak authentication protocols such as HTTP Basic Authentication.

	      Retry indefinitely on HTTP proxy errors.	If an HTTP proxy error
	      occurs, simulate a SIGUSR1 reset.

       --http-proxy-timeout n
	      Set proxy	timeout	to n seconds, default=5.

       --http-proxy-option type	[parm]
	      Set  extended  HTTP  proxy  options.   Repeat  to	 set  multiple

	      VERSION  version	--  Set	 HTTP  version	 number	  to   version

	      AGENT  user-agent	-- Set HTTP "User-Agent" string	to user-agent.

       --socks-proxy server [port] [authfile]
	      Connect to remote	host through a Socks5 proxy at address	server
	      and  port	 port  (default=1080).	 authfile (optional) is	a file
	      containing a username and	password on 2  lines,  or  "stdin"  to
	      prompt from console.

	      Retry  indefinitely  on  Socks  proxy  errors.  If a Socks proxy
	      error occurs, simulate a SIGUSR1 reset.

       --resolv-retry n
	      If hostname resolve fails	for --remote, retry resolve for	n sec-
	      onds before failing.

	      Set n to "infinite" to retry indefinitely.

	      By default, --resolv-retry infinite is enabled.  You can disable
	      by setting n=0.

	      Allow remote peer	to change its IP address and/or	 port  number,
	      such  as	due  to	 DHCP  (this is	the default if --remote	is not
	      used).  --float when specified with --remote allows  an  OpenVPN
	      session  to initially connect to a peer at a known address, how-
	      ever if packets arrive from a new	address	and pass all authenti-
	      cation  tests, the new address will take control of the session.
	      This is useful when you are connecting to	a peer which  holds  a
	      dynamic address such as a	dial-in	user or	DHCP client.

	      Essentially, --float tells OpenVPN to accept authenticated pack-
	      ets from any address, not	only the address which	was  specified
	      in the --remote option.

       --ipchange cmd
	      Run  command cmd when our	remote ip-address is initially authen-
	      ticated or changes.

	      cmd consists of  a  path	to  script  (or	 executable  program),
	      optionally  followed by arguments. The path and arguments	may be
	      single- or double-quoted and/or escaped using a  backslash,  and
	      should be	separated by one or more spaces.

	      When  cmd	is executed two	arguments are appended after any argu-
	      ments specified in cmd , as follows:

	      cmd ip_address port_number

	      Don't use	--ipchange in --mode server mode.  Use a --client-con-
	      nect script instead.

	      See  the	"Environmental Variables" section below	for additional
	      parameters passed	as environmental variables.

	      If you are running in a dynamic IP address environment where the
	      IP addresses of either peer could	change without notice, you can
	      use this script, for example, to edit the	/etc/hosts  file  with
	      the  current  address of the peer.  The script will be run every
	      time the remote peer changes its IP address.

	      Similarly	if our IP address changes due to DHCP, we should  con-
	      figure  our IP address change script (see	man page for dhcpcd(8)
	      )	to deliver a SIGHUP or SIGUSR1	signal	to  OpenVPN.   OpenVPN
	      will  then  reestablish  a  connection  with  its	 most recently
	      authenticated peer on its	new IP address.

       --port port
	      TCP/UDP port number or port name for both	local and remote (sets
	      both  --lport  and  --rport options to given port).  The current
	      default of 1194 represents the official IANA port	number assign-
	      ment  for	 OpenVPN  and  has been	used since version 2.0-beta17.
	      Previous versions	used port 5000 as the default.

       --lport port
	      Set local	TCP/UDP	port number or name.  Cannot be	used  together
	      with --nobind option.

       --rport port
	      Set TCP/UDP port number or name used by the --remote option. The
	      port can also be set directly using the --remote option.

       --bind Bind to local address and	port. This is the default  unless  any
	      of  --proto tcp-client , --http-proxy or --socks-proxy are used.

	      Do not bind to local address and port.  The IP stack will	 allo-
	      cate  a  dynamic port for	returning packets.  Since the value of
	      the dynamic port could not be known in advance by	a  peer,  this
	      option  is only suitable for peers which will be initiating con-
	      nections by using	the --remote option.

       --dev tunX | tapX | null
	      TUN/TAP virtual network device ( X can be	omitted	for a  dynamic

	      See  examples  section  below for	an example on setting up a TUN

	      You must use either tun devices on both ends of  the  connection
	      or  tap devices on both ends.  You cannot	mix them, as they rep-
	      resent different underlying network layers.

	      tun devices encapsulate IPv4 or IPv6 (OSI	 Layer	3)  while  tap
	      devices encapsulate Ethernet 802.3 (OSI Layer 2).

       --dev-type device-type
	      Which  device type are we	using?	device-type should be tun (OSI
	      Layer 3) or tap (OSI Layer 2).  Use  this	 option	 only  if  the
	      TUN/TAP device used with --dev does not begin with tun or	tap.

       --topology mode
	      Configure	 virtual addressing topology when running in --dev tun
	      mode.  This directive has	no meaning in --dev  tap  mode,	 which
	      always uses a subnet topology.

	      If  you  set  this  directive  on	 the  server, the --server and
	      --server-bridge directives will automatically push  your	chosen
	      topology setting to clients as well.  This directive can also be
	      manually pushed to clients.   Like  the  --dev  directive,  this
	      directive	must always be compatible between client and server.

	      mode can be one of:

	      net30  --	 Use  a	point-to-point topology, by allocating one /30
	      subnet per client.  This is  designed  to	 allow	point-to-point
	      semantics	 when  some  or	all of the connecting clients might be
	      Windows systems.	This is	the default on OpenVPN 2.0.

	      p2p -- Use a point-to-point topology where the  remote  endpoint
	      of  the  client's	 tun interface always points to	the local end-
	      point of the server's tun	interface.  This mode allocates	a sin-
	      gle IP address per connecting client.  Only use when none	of the
	      connecting clients are Windows systems.  This mode is  function-
	      ally equivalent to the --ifconfig-pool-linear directive which is
	      available	in OpenVPN 2.0 and is now deprecated.

	      subnet --	Use a subnet rather than a point-to-point topology  by
	      configuring the tun interface with a local IP address and	subnet
	      mask, similar to the topology used in  --dev  tap	 and  ethernet
	      bridging mode.  This mode	allocates a single IP address per con-
	      necting client and works on Windows  as  well.   Only  available
	      when  server  and	 clients are OpenVPN 2.1 or higher, or OpenVPN
	      2.0.x which has been manually patched with the --topology	direc-
	      tive code.  When used on Windows,	requires version 8.2 or	higher
	      of the TAP-Win32 driver.	When used on *nix, requires  that  the
	      tun  driver  supports an ifconfig(8) command which sets a	subnet
	      instead of a remote endpoint IP address.

	      This option exists in OpenVPN 2.1	or higher.

	      Note: Using --topology subnet changes the	interpretation of  the
	      arguments	 of  --ifconfig	 to  mean "address netmask", no	longer
	      "local remote".

	      Build a tun link capable of forwarding IPv6 traffic.  Should  be
	      used  in	conjunction  with  --dev tun or	--dev tunX.  A warning
	      will be displayed	if no specific IPv6 TUN	support	 for  your  OS
	      has been compiled	into OpenVPN.

	      See below	for further IPv6-related configuration options.

       --dev-node node
	      Explicitly  set  the device node rather than using /dev/net/tun,
	      /dev/tun,	/dev/tap, etc.	If OpenVPN cannot figure  out  whether
	      node  is	a TUN or TAP device based on the name, you should also
	      specify --dev-type tun or	--dev-type tap.

	      Under Mac	OS X this option can be	used to	 specify  the  default
	      tun  implementation.  Using  --dev-node utun forces usage	of the
	      native Darwin tun	kernel support.	Use --dev-node utunN to	select
	      a	  specific   utun   instance.  To  force  using	 the  tun.kext
	      (/dev/tunX)  use	--dev-node  tun.   When	  not	specifying   a
	      --dev-node  option openvpn will first try	to open	utun, and fall
	      back to tun.kext.

	      On Windows systems, select the TAP-Win32 adapter which is	 named
	      node in the Network Connections Control Panel or the raw GUID of
	      the adapter enclosed  by	braces.	  The  --show-adapters	option
	      under  Windows  can also be used to enumerate all	available TAP-
	      Win32 adapters and will show both	the network  connections  con-
	      trol panel name and the GUID for each TAP-Win32 adapter.

       --lladdr	address
	      Specify  the  link layer address,	more commonly known as the MAC
	      address.	Only applied to	TAP devices.

       --iproute cmd
	      Set alternate command to execute	instead	 of  default  iproute2
	      command.	 May  be  used in order	to execute OpenVPN in unprivi-
	      leged environment.

       --ifconfig l rn
	      Set TUN/TAP adapter parameters.  l is  the  IP  address  of  the
	      local  VPN endpoint.  For	TUN devices in point-to-point mode, rn
	      is the IP	address	of the remote VPN endpoint.  For TAP  devices,
	      or  TUN  devices	used  with --topology subnet, rn is the	subnet
	      mask of the virtual network segment which	is  being  created  or
	      connected	to.

	      For TUN devices, which facilitate	virtual	point-to-point IP con-
	      nections (when used in --topology	net30 or p2p mode), the	proper
	      usage of --ifconfig is to	use two	private	IP addresses which are
	      not a member of any existing subnet which	is  in	use.   The  IP
	      addresses	 may  be  consecutive  and  should  have  their	 order
	      reversed on the remote peer.  After the VPN is  established,  by
	      pinging rn, you will be pinging across the VPN.

	      For  TAP	devices,  which	 provide the ability to	create virtual
	      ethernet segments, or TUN	 devices  in  --topology  subnet  mode
	      (which create virtual "multipoint	networks"), --ifconfig is used
	      to set an	IP address and subnet mask just	as a physical ethernet
	      adapter would be similarly configured.  If you are attempting to
	      connect to a remote ethernet bridge, the IP address  and	subnet
	      should  be set to	values which would be valid on the the bridged
	      ethernet segment (note also that DHCP can	be used	for  the  same

	      This  option,  while  primarily a	proxy for the ifconfig(8) com-
	      mand, is designed	to simplify TUN/TAP  tunnel  configuration  by
	      providing	 a standard interface to the different ifconfig	imple-
	      mentations on different platforms.

	      --ifconfig parameters which are IP addresses can also be	speci-
	      fied as a	DNS or /etc/hosts file resolvable name.

	      For TAP devices, --ifconfig should not be	used if	the TAP	inter-
	      face will	be getting an IP address lease from a DHCP server.

	      Don't actually execute  ifconfig/netsh  commands,	 instead  pass
	      --ifconfig  parameters to	scripts	using environmental variables.

	      Don't  output  an	 options  consistency  check  warning  if  the
	      --ifconfig  option  on this side of the connection doesn't match
	      the remote side.	This is	useful when you	 want  to  retain  the
	      overall  benefits	 of  the  options  consistency check (also see
	      --disable-occ option) while only disabling the  ifconfig	compo-
	      nent of the check.

	      For  example,  if	 you have a configuration where	the local host
	      uses --ifconfig but the  remote  host  does  not,	 use  --ifcon-
	      fig-nowarn on the	local host.

	      This  option  will also silence warnings about potential address
	      conflicts	which occasionally annoy  more	experienced  users  by
	      triggering "false	positive" warnings.

       --route network/IP [netmask] [gateway] [metric]
	      Add  route  to  routing  table  after connection is established.
	      Multiple routes can be specified.	 Routes	will be	 automatically
	      torn down	in reverse order prior to TUN/TAP device close.

	      This  option is intended as a convenience	proxy for the route(8)
	      shell command, while at the same time providing portable	seman-
	      tics across OpenVPN's platform space.

	      netmask default --

	      gateway  default	--  taken  from	 --route-gateway or the	second
	      parameter	to --ifconfig when --dev tun is	specified.

	      metric default --	taken from --route-metric otherwise 0.

	      The default can be specified by leaving an option	blank or  set-
	      ting it to "default".

	      The  network  and	 gateway parameters can	also be	specified as a
	      DNS or /etc/hosts	file resolvable	name, or as one	of three  spe-
	      cial keywords:

	      vpn_gateway  --  The remote VPN endpoint address (derived	either
	      from --route-gateway or the second parameter to --ifconfig  when
	      --dev tun	is specified).

	      net_gateway  --  The  pre-existing IP default gateway, read from
	      the routing table	(not supported on all OSes).

	      remote_host -- The --remote address if OpenVPN is	being  run  in
	      client mode, and is undefined in server mode.

       --max-routes n
	      Allow  a	maximum	 number	 of n --route options to be specified,
	      either in	the local configuration	file, or pulled	from an	 Open-
	      VPN server.  By default, n=100.

       --route-gateway gw|'dhcp'
	      Specify a	default	gateway	gw for use with	--route.

	      If  dhcp is specified as the parameter, the gateway address will
	      be extracted from	a DHCP negotiation with	 the  OpenVPN  server-
	      side LAN.

       --route-metric m
	      Specify a	default	metric m for use with --route.

       --route-delay [n] [w]
	      Delay  n	seconds	 (default=0)  after  connection	establishment,
	      before adding routes. If n is 0, routes will  be	added  immedi-
	      ately  upon connection establishment.  If	--route-delay is omit-
	      ted, routes will be added	immediately after TUN/TAP device  open
	      and  --up	 script	execution, before any --user or	--group	privi-
	      lege downgrade (or --chroot execution.)

	      This option is designed to be useful in scenarios	where DHCP  is
	      used to set tap adapter addresses.  The delay will give the DHCP
	      handshake	time to	complete before	routes are added.

	      On Windows, --route-delay	tries to be more intelligent by	 wait-
	      ing  w  seconds  (w=30  by default) for the TAP-Win32 adapter to
	      come up before adding routes.

       --route-up cmd
	      Run  command  cmd	  after	  routes   are	 added,	  subject   to

	      cmd  consists  of	 a  path  to  script  (or executable program),
	      optionally followed by arguments.	The path and arguments may  be
	      single-  or  double-quoted and/or	escaped	using a	backslash, and
	      should be	separated by one or more spaces.

	      See the "Environmental Variables"	section	below  for  additional
	      parameters passed	as environmental variables.

       --route-pre-down	cmd
	      Run command cmd before routes are	removed	upon disconnection.

	      cmd  consists  of	 a  path  to  script  (or executable program),
	      optionally followed by arguments.	The path and arguments may  be
	      single-  or  double-quoted and/or	escaped	using a	backslash, and
	      should be	separated by one or more spaces.

	      See the "Environmental Variables"	section	below  for  additional
	      parameters passed	as environmental variables.

	      Don't  add  or remove routes automatically.  Instead pass	routes
	      to --route-up script using environmental variables.

	      When used	with --client or  --pull,  accept  options  pushed  by
	      server  EXCEPT  for  routes,  block-outside-dns and dhcp options
	      like DNS servers.

	      When used	on the client, this option effectively bars the	server
	      from  adding  routes to the client's routing table, however note
	      that this	option still allows the	server to set the TCP/IP prop-
	      erties of	the client's TUN/TAP interface.

	      Allow  client  to	 pull DNS names	from server (rather than being
	      limited  to   IP	 address)   for	  --ifconfig,	--route,   and

       --client-nat snat|dnat network netmask alias
	      This  pushable  client option sets up a stateless	one-to-one NAT
	      rule on packet addresses (not ports), and	 is  useful  in	 cases
	      where  routes  or	 ifconfig  settings pushed to the client would
	      create an	IP numbering conflict.

	      network/netmask (for  example  defines
	      the  local view of a resource from the client perspective, while
	      alias/netmask (for example  defines  the
	      remote view from the server perspective.

	      Use snat (source NAT) for	resources owned	by the client and dnat
	      (destination NAT)	for remote resources.

	      Set --verb 6 for debugging info showing  the  transformation  of
	      src/dest addresses in packets.

       --redirect-gateway flags...
	      Automatically  execute routing commands to cause all outgoing IP
	      traffic to be redirected over the	VPN.  This  is	a  client-side

	      This option performs three steps:

	      (1)  Create  a  static route for the --remote address which for-
	      wards to the pre-existing	default	gateway.  This is done so that
	      (3) will not create a routing loop.

	      (2) Delete the default gateway route.

	      (3)  Set	the new	default	gateway	to be the VPN endpoint address
	      (derived either from --route-gateway or the second parameter  to
	      --ifconfig when --dev tun	is specified).

	      When  the	 tunnel	 is  torn  down,  all  of  the above steps are
	      reversed so that the original default route is restored.

	      Option flags:

	      local -- Add the local flag if both OpenVPN servers are directly
	      connected	via a common subnet, such as with wireless.  The local
	      flag will	cause step 1 above to be omitted.

	      autolocal	-- Try to automatically	determine  whether  to	enable
	      local flag above.

	      def1  --	Use this flag to override the default gateway by using	and	rather than	This  has  the
	      benefit  of  overriding  but not wiping out the original default

	      bypass-dhcp -- Add a direct route	to the DHCP server (if	it  is
	      non-local)  which	 bypasses  the	tunnel	(Available  on Windows
	      clients, may not be available on non-Windows clients).

	      bypass-dns -- Add	a direct route to the DNS server(s)  (if  they
	      are  non-local)  which bypasses the tunnel (Available on Windows
	      clients, may not be available on non-Windows clients).

	      block-local -- Block access to local  LAN	 when  the  tunnel  is
	      active, except for the LAN gateway itself.  This is accomplished
	      by routing the local LAN (except for the	LAN  gateway  address)
	      into the tunnel.

       --link-mtu n
	      Sets  an	upper  bound on	the size of UDP	packets	which are sent
	      between OpenVPN peers.  It's best	 not  to  set  this  parameter
	      unless you know what you're doing.

       --redirect-private [flags]
	      Like  --redirect-gateway,	but omit actually changing the default
	      gateway.	Useful when pushing private subnets.

       --tun-mtu n
	      Take the TUN device MTU to be n and derive the link MTU from  it
	      (default=1500).	In most	cases, you will	probably want to leave
	      this parameter set to its	default	value.

	      The MTU (Maximum Transmission Units)  is	the  maximum  datagram
	      size  in	bytes  that can	be sent	unfragmented over a particular
	      network path.  OpenVPN requires that packets on the  control  or
	      data channels be sent unfragmented.

	      MTU problems often manifest themselves as	connections which hang
	      during periods of	active usage.

	      It's best	to use the --fragment and/or --mssfix options to  deal
	      with MTU sizing issues.

       --tun-mtu-extra n
	      Assume  that  the	TUN/TAP	device might return as many as n bytes
	      more than	the --tun-mtu size on read.  This  parameter  defaults
	      to 0, which is sufficient	for most TUN devices.  TAP devices may
	      introduce	additional overhead in excess of the MTU size,	and  a
	      setting  of  32  is the default when TAP devices are used.  This
	      parameter	only controls internal OpenVPN buffer sizing, so there
	      is  no  transmission  overhead  associated  with	using a	larger

       --mtu-disc type
	      Should we	do Path	MTU discovery on TCP/UDP channel?   Only  sup-
	      ported  on OSes such as Linux that supports the necessary	system
	      call to set.

	      'no' -- Never send DF (Don't Fragment) frames
	      'maybe' -- Use per-route hints
	      'yes' -- Always DF (Don't	Fragment)

	      To empirically  measure  MTU  on	connection  startup,  add  the
	      --mtu-test option	to your	configuration.	OpenVPN	will send ping
	      packets of various sizes to the  remote  peer  and  measure  the
	      largest	packets	  which	  were	 successfully  received.   The
	      --mtu-test process normally takes	about 3	minutes	to complete.

       --fragment max
	      Enable internal datagram fragmentation so	that no	UDP  datagrams
	      are sent which are larger	than max bytes.

	      The  max	parameter  is  interpreted  in	the  same  way	as the
	      --link-mtu parameter, i.e. the UDP packet	size after  encapsula-
	      tion  overhead  has  been	 added	in,  but not including the UDP
	      header itself.

	      The --fragment option only makes sense when you  are  using  the
	      UDP protocol ( --proto udp ).

	      --fragment adds 4	bytes of overhead per datagram.

	      See the --mssfix option below for	an important related option to

	      It should	also be	noted that this	option is not meant to replace
	      UDP  fragmentation at the	IP stack level.	 It is only meant as a
	      last resort when path  MTU  discovery  is	 broken.   Using  this
	      option is	less efficient than fixing path	MTU discovery for your
	      IP link and using	native IP fragmentation	instead.

	      Having said that,	there are circumstances	where using  OpenVPN's
	      internal	fragmentation capability may be	your only option, such
	      as tunneling a UDP multicast stream  which  requires  fragmenta-

       --mssfix	max
	      Announce	to  TCP	 sessions  running  over  the tunnel that they
	      should limit their send packet sizes such	that after OpenVPN has
	      encapsulated  them,  the	resulting UDP packet size that OpenVPN
	      sends to its peer	will not exceed	max bytes. The	default	 value
	      is 1450.

	      The  max	parameter  is  interpreted  in	the  same  way	as the
	      --link-mtu parameter, i.e. the UDP packet	size after  encapsula-
	      tion  overhead  has  been	 added	in,  but not including the UDP
	      header itself. Resulting packet would be at most 28 bytes	larger
	      for  IPv4	and 48 bytes for IPv6 (20/40 bytes for IP header and 8
	      bytes for	UDP header). Default value of 1450 allows IPv4 packets
	      to be transmitted	over a link with MTU 1473 or higher without IP
	      level fragmentation.

	      The --mssfix option only makes sense when	you are	using the  UDP
	      protocol	for  OpenVPN peer-to-peer communication, i.e.  --proto

	      --mssfix and --fragment can  be  ideally	used  together,	 where
	      --mssfix	will try to keep TCP from needing packet fragmentation
	      in the first place, and if big packets come through anyhow (from
	      protocols	 other	than TCP), --fragment will internally fragment

	      Both --fragment and --mssfix are designed	to work	 around	 cases
	      where  Path  MTU discovery is broken on the network path between
	      OpenVPN peers.

	      The usual	symptom	of such	a breakdown is an  OpenVPN  connection
	      which  successfully starts, but then stalls during active	usage.

	      If --fragment and	--mssfix are used together, --mssfix will take
	      its default max parameter	from the --fragment max	option.

	      Therefore,  one  could lower the maximum UDP packet size to 1300
	      (a good first try	for solving MTU-related	 connection  problems)
	      with the following options:

	      --tun-mtu	1500 --fragment	1300 --mssfix

       --sndbuf	size
	      Set  the TCP/UDP socket send buffer size.	 Defaults to operation
	      system default.

       --rcvbuf	size
	      Set the TCP/UDP socket receive buffer size.  Defaults to	opera-
	      tion system default.

       --mark value
	      Mark encrypted packets being sent	with value. The	mark value can
	      be matched in policy routing and packetfilter rules. This	option
	      is  only	supported in Linux and does nothing on other operating

       --socket-flags flags...
	      Apply the	given flags to the  OpenVPN  transport	socket.	  Cur-
	      rently, only TCP_NODELAY is supported.

	      The  TCP_NODELAY	socket	flag is	useful in TCP mode, and	causes
	      the kernel to send tunnel	packets	immediately over the TCP  con-
	      nection  without	trying to group	several	smaller	packets	into a
	      larger packet.  This can result in a considerably	improvement in

	      This  option  is	pushable  from server to client, and should be
	      used on both client and server for maximum effect.

       --txqueuelen n
	      (Linux only) Set the TX queue length on the  TUN/TAP  interface.
	      Currently	defaults to 100.

       --shaper	n
	      Limit bandwidth of outgoing tunnel data to n bytes per second on
	      the TCP/UDP port.	 Note that this	will only work if mode is  set
	      to  p2p.	If you want to limit the bandwidth in both directions,
	      use this option on both peers.

	      OpenVPN uses the following algorithm to implement	traffic	 shap-
	      ing: Given a shaper rate of n bytes per second, after a datagram
	      write of b bytes is queued on the	TCP/UDP	port, wait  a  minimum
	      of (b / n) seconds before	queuing	the next write.

	      It  should  be  noted  that  OpenVPN  supports  multiple tunnels
	      between the same two peers, allowing you to construct full-speed
	      and reduced bandwidth tunnels at the same	time, routing low-pri-
	      ority data such as off-site backups over the  reduced  bandwidth
	      tunnel, and other	data over the full-speed tunnel.

	      Also  note  that for low bandwidth tunnels (under	1000 bytes per
	      second), you should probably use lower MTU values	as  well  (see
	      above),  otherwise  the  packet latency will grow	so large as to
	      trigger timeouts in the TLS layer	and  TCP  connections  running
	      over the tunnel.

	      OpenVPN allows n to be between 100 bytes/sec and 100 Mbytes/sec.

       --inactive n [bytes]
	      Causes OpenVPN to	exit after n  seconds  of  inactivity  on  the
	      TUN/TAP  device. The time	length of inactivity is	measured since
	      the last incoming	or outgoing tunnel packet.  The	default	 value
	      is 0 seconds, which disables this	feature.

	      If  the  optional	bytes parameter	is included, exit if less than
	      bytes of combined	in/out traffic are  produced  on  the  tun/tap
	      device in	n seconds.

	      In  any  case,  OpenVPN's	 internal ping packets (which are just
	      keepalives) and TLS control packets are not  considered  "activ-
	      ity",  nor  are they counted as traffic, as they are used	inter-
	      nally by OpenVPN and are not an indication of actual user	activ-

       --ping n
	      Ping  remote over	the TCP/UDP control channel if no packets have
	      been sent	for at least n seconds (specify	--ping on  both	 peers
	      to  cause	ping packets to	be sent	in both	directions since Open-
	      VPN ping packets are not echoed like  IP	ping  packets).	  When
	      used   in	  one  of  OpenVPN's  secure  modes  (where  --secret,
	      --tls-server, or --tls-client is	specified),  the  ping	packet
	      will be cryptographically	secure.

	      This option has two intended uses:

	      (1)  Compatibility  with	stateful firewalls.  The periodic ping
	      will ensure that a stateful firewall rule	which  allows  OpenVPN
	      UDP packets to pass will not time	out.

	      (2)  To  provide a basis for the remote to test the existence of
	      its peer using the --ping-exit option.

       --ping-exit n
	      Causes OpenVPN to	exit after n seconds pass without reception of
	      a	ping or	other packet from remote.  This	option can be combined
	      with --inactive, --ping, and --ping-exit to create a  two-tiered
	      inactivity disconnect.

	      For example,

	      openvpn [options...] --inactive 3600 --ping 10 --ping-exit 60

	      when  used  on  both  peers will cause OpenVPN to	exit within 60
	      seconds if its peer disconnects, but will	exit after one hour if
	      no actual	tunnel data is exchanged.

       --ping-restart n
	      Similar  to  --ping-exit,	 but trigger a SIGUSR1 restart after n
	      seconds pass without reception of	a ping or  other  packet  from

	      This  option  is	useful	in  cases  where the remote peer has a
	      dynamic IP address and a low-TTL DNS name	is used	to  track  the
	      IP  address  using  a  service  such  as + a
	      dynamic DNS client such as ddclient.

	      If the peer cannot be reached,  a	 restart  will	be  triggered,
	      causing  the  hostname  used with	--remote to be re-resolved (if
	      --resolv-retry is	also specified).

	      In server	mode, --ping-restart, --inactive, or any other type of
	      internally generated signal will always be applied to individual
	      client instance objects, never to	 whole	server	itself.	  Note
	      also  in	server mode that any internally	generated signal which
	      would normally cause a restart, will cause the deletion  of  the
	      client instance object instead.

	      In  client mode, the --ping-restart parameter is set to 120 sec-
	      onds by default.	This default will hold until the client	 pulls
	      a	 replacement  value  from the server, based on the --keepalive
	      setting in the server configuration.  To disable the 120	second
	      default, set --ping-restart 0 on the client.

	      See the signals section below for	more information on SIGUSR1.

	      Note  that the behavior of SIGUSR1 can be	modified by the	--per-
	      sist-tun,	  --persist-key,   --persist-local-ip,	 and	--per-
	      sist-remote-ip options.

	      Also  note  that	--ping-exit  and  --ping-restart  are mutually
	      exclusive	and cannot be used together.

       --keepalive n m
	      A	helper directive designed to simplify the expression of	--ping
	      and --ping-restart in server mode	configurations.

	      The  server  timeout  is set twice the value of the second argu-
	      ment.  This ensures that a timeout is detected  on  client  side
	      before the server	side drops the connection.

	      For example, --keepalive 10 60 expands as	follows:

		   if mode server:
		     ping 10
		     ping-restart 120
		     push "ping	10"
		     push "ping-restart	60"
		     ping 10
		     ping-restart 60

	      Run  the	--ping-exit  /	--ping-restart timer only if we	have a
	      remote address.  Use this	option if you are starting the	daemon
	      in listen	mode (i.e. without an explicit --remote	peer), and you
	      don't want to start clocking timeouts until a remote  peer  con-

	      Don't  close  and	 reopen	 TUN/TAP device	or run up/down scripts
	      across SIGUSR1 or	--ping-restart restarts.

	      SIGUSR1 is a restart signal similar to SIGHUP, but which	offers
	      finer-grained control over reset options.

	      Don't re-read key	files across SIGUSR1 or	--ping-restart.

	      This option can be combined with --user nobody to	allow restarts
	      triggered	by the SIGUSR1 signal.	 Normally  if  you  drop  root
	      privileges  in  OpenVPN, the daemon cannot be restarted since it
	      will now be unable to re-read protected key files.

	      This option solves the problem by	persisting keys	across SIGUSR1
	      resets, so they don't need to be re-read.

	      Preserve	initially  resolved  local  IP address and port	number
	      across SIGUSR1 or	--ping-restart restarts.

	      Preserve most recently authenticated remote IP address and  port
	      number across SIGUSR1 or --ping-restart restarts.

	      Disable paging by	calling	the POSIX mlockall function.  Requires
	      that OpenVPN be initially	run as root (though OpenVPN can	subse-
	      quently downgrade	its UID	using the --user option).

	      Using  this option ensures that key material and tunnel data are
	      never written to disk due	to virtual  memory  paging  operations
	      which  occur  under  most	 modern	operating systems.  It ensures
	      that even	if an attacker was able	to crack the box running Open-
	      VPN,  he	would  not  be	able  to  scan the system swap file to
	      recover previously used ephemeral	keys, which  are  used	for  a
	      period of	time governed by the --reneg options (see below), then
	      are discarded.

	      The downside of using --mlock is that it will reduce the	amount
	      of physical memory available to other applications.

       --up cmd
	      Run command cmd after successful TUN/TAP device open (pre	--user
	      UID change).

	      cmd consists of  a  path	to  script  (or	 executable  program),
	      optionally  followed by arguments. The path and arguments	may be
	      single- or double-quoted and/or escaped using a  backslash,  and
	      should be	separated by one or more spaces.

	      The  up  command	is  useful for specifying route	commands which
	      route IP traffic destined	for private subnets which exist	at the
	      other end	of the VPN connection into the tunnel.

	      For --dev	tun execute as:

	      cmd    tun_dev   tun_mtu	 link_mtu   ifconfig_local_ip	ifcon-
	      fig_remote_ip [ init | restart ]

	      For --dev	tap execute as:

	      cmd tap_dev tap_mtu link_mtu ifconfig_local_ip  ifconfig_netmask
	      [	init | restart ]

	      See  the	"Environmental Variables" section below	for additional
	      parameters passed	as environmental variables.

	      Note that	if cmd includes	arguments, all OpenVPN-generated argu-
	      ments  will  be  appended	to them	to build an argument list with
	      which the	executable will	be called.

	      Typically, cmd will run a	script to add routes to	the tunnel.

	      Normally the up script is	called after  the  TUN/TAP  device  is
	      opened.  In this context,	the last command line parameter	passed
	      to the script will be init.  If the --up-restart option is  also
	      used,  the  up  script  will  be called for restarts as well.  A
	      restart is considered to be a partial reinitialization of	 Open-
	      VPN  where  the TUN/TAP instance is preserved (the --persist-tun
	      option will enable such preservation).  A	restart	can be	gener-
	      ated by a	SIGUSR1	signal,	a --ping-restart timeout, or a connec-
	      tion reset when the TCP protocol is  enabled  with  the  --proto
	      option.	If  a restart occurs, and --up-restart has been	speci-
	      fied, the	up script will be called  with	restart	 as  the  last

	      NOTE: on restart,	OpenVPN	will not pass the full set of environ-
	      ment variables to	the script.   Namely,  everything  related  to
	      routing  and gateways will not be	passed,	as nothing needs to be
	      done anyway - all	the routing setup is already in	place.	 Addi-
	      tionally,	 the  up-restart  script  will run with	the downgraded
	      UID/GID settings (if configured).

	      The following standalone example shows how the --up  script  can
	      be called	in both	an initialization and restart context.	(NOTE:
	      for security reasons, don't run the following example unless UDP
	      port  9999  is blocked by	your firewall.	Also, the example will
	      run indefinitely,	so you should abort with control-c).

	      openvpn --dev tun	--port 9999 --verb 4  --ping-restart  10  --up
	      'echo up'	--down 'echo down' --persist-tun --up-restart

	      Note  that  OpenVPN also provides	the --ifconfig option to auto-
	      matically	ifconfig the  TUN  device,  eliminating	 the  need  to
	      define  an --up script, unless you also want to configure	routes
	      in the --up script.

	      If --ifconfig is also specified, OpenVPN will pass the  ifconfig
	      local  and  remote  endpoints  on	 the  command line to the --up
	      script so	that they can be used to configure routes such as:

	      route add	-net netmask gw $5

	      Delay TUN/TAP open and  possible	--up  script  execution	 until
	      after TCP/UDP connection establishment with peer.

	      In  --proto  udp	mode, this option normally requires the	use of
	      --ping to	allow  connection  initiation  to  be  sensed  in  the
	      absence  of  tunnel data,	since UDP is a "connectionless"	proto-

	      On Windows, this option will delay  the  TAP-Win32  media	 state
	      transitioning  to	 "connected"  until  connection	establishment,
	      i.e. the receipt of the  first  authenticated  packet  from  the

       --down cmd
	      Run  command  cmd	 after	TUN/TAP	 device	close (post --user UID
	      change and/or --chroot ).	 cmd consists of a path	to script  (or
	      executable  program), optionally followed	by arguments. The path
	      and arguments may	be single-  or	double-quoted  and/or  escaped
	      using  a	backslash, and should be separated by one or more spa-

	      Called with the same parameters and environmental	 variables  as
	      the --up option above.

	      Note  that  if  you  reduce  privileges  by  using --user	and/or
	      --group, your --down script will also run	at reduced  privilege.

	      Call --down cmd/script before, rather than after,	TUN/TAP	close.

	      Enable the --up and --down scripts to be called for restarts  as
	      well  as	initial	 program start.	 This option is	described more
	      fully above in the --up option documentation.

       --setenv	name value
	      Set a  custom  environmental  variable  name=value  to  pass  to

       --setenv	FORWARD_COMPATIBLE 1
	      Relax  config  file  syntax  checking so that unknown directives
	      will trigger a warning but not a fatal error, on the  assumption
	      that  a given unknown directive might be valid in	future OpenVPN

	      This option should be used with caution, as there	are good secu-
	      rity reasons for having OpenVPN fail if it detects problems in a
	      config file.  Having said	that,  there  are  valid  reasons  for
	      wanting new software features to gracefully degrade when encoun-
	      tered by older software versions.

	      It is also possible to tag a single directive so as not to trig-
	      ger  a  fatal  error  if	the directive isn't recognized.	 To do
	      this, prepend the	following before the directive:	setenv opt

	      Versions prior to	OpenVPN	2.3.3 will always ignore  options  set
	      with the setenv opt directive.

	      See also --ignore-unknown-option

       --setenv-safe name value
	      Set  a  custom environmental variable OPENVPN_name=value to pass
	      to script.

	      This directive is	 designed  to  be  pushed  by  the  server  to
	      clients,	and  the prepending of "OPENVPN_" to the environmental
	      variable is a safety precaution to prevent  a  LD_PRELOAD	 style
	      attack from a malicious or compromised server.

       --ignore-unknown-option opt1 opt2 opt3 ... optN
	      When one of options opt1 ... optN	is encountered in the configu-
	      ration file the configuration file parsing does not fail if this
	      OpenVPN	version	  does	 not   support	the  option.  Multiple
	      --ignore-unknown-option options can be given to support a	larger
	      number of	options	to ignore.

	      This option should be used with caution, as there	are good secu-
	      rity reasons for having OpenVPN fail if it detects problems in a
	      config file. Having said that, there are valid reasons for want-
	      ing new software features	to gracefully degrade when encountered
	      by older software	versions.

	      --ignore-unknown-option is available since OpenVPN 2.3.3.

       --script-security level
	      This  directive offers policy-level control over OpenVPN's usage
	      of external programs and scripts.	 Lower level values  are  more
	      restrictive,  higher  values  are	more permissive.  Settings for

	      0	-- Strictly no calling of external programs.
	      1	-- (Default) Only call built-in	executables such as  ifconfig,
	      ip, route, or netsh.
	      2	 --  Allow  calling  of	 built-in executables and user-defined
	      3	-- Allow passwords to be passed	to scripts  via	 environmental
	      variables	(potentially unsafe).

	      OpenVPN  releases	before v2.3 also supported a method flag which
	      indicated	how OpenVPN should call	external commands and scripts.
	      This could be either execve or system.  As of OpenVPN v2.3, this
	      flag is no longer	 accepted.   In	 most  *nix  environments  the
	      execve() approach	has been used without any issues.

	      Some  directives	such as	--up allow options to be passed	to the
	      external script. In these	cases make sure	the script  name  does
	      not  contain  any	 spaces	or the configuration parser will choke
	      because it can't determine where the script name ends and	script
	      options start.

	      To run scripts in	Windows	in earlier OpenVPN versions you	needed
	      to either	add a full path	to the script  interpreter  which  can
	      parse  the  script  or use the system flag to run	these scripts.
	      As of OpenVPN v2.3 it is now a strict requirement	to  have  full
	      path  to	the  script  interpreter  when running non-executables
	      files.  This is not needed for executable	files, such  as	 .exe,
	      .com,  .bat  or  .cmd  files.  For example, if you have a	Visual
	      Basic script, you	must use this syntax now:

		  --up 'C:\\Windows\\System32\\wscript.exe C:\\Program\	Files\\OpenVPN\\config\\my-up-script.vbs'

	      Please note the single quote marks and the escaping of the back-
	      slashes (\) and the space	character.

	      The reason the support for the system flag was removed is	due to
	      the security implications	with shell expansions  when  executing
	      scripts via the system() call.

	      Don't  output  a	warning	 message if option inconsistencies are
	      detected between peers.  An example of an	 option	 inconsistency
	      would be where one peer uses --dev tun while the other peer uses
	      --dev tap.

	      Use of this option is discouraged, but is	provided as  a	tempo-
	      rary  fix	 in  situations	where a	recent version of OpenVPN must
	      connect to an old	version.

       --user user
	      Change the user ID of the	OpenVPN	process	to user	after initial-
	      ization,	dropping  privileges  in  the process.	This option is
	      useful to	protect	the system in  the  event  that	 some  hostile
	      party  was  able	to gain	control	of an OpenVPN session.	Though
	      OpenVPN's	security features make this unlikely, it  is  provided
	      as a second line of defense.

	      By  setting  user	 to nobody or somebody similarly unprivileged,
	      the hostile party	would be limited in  what  damage  they	 could
	      cause.   Of  course  once	 you  take away	privileges, you	cannot
	      return them to an	OpenVPN	session.   This	 means,	 for  example,
	      that  if you want	to reset an OpenVPN daemon with	a SIGUSR1 sig-
	      nal (for example in response to a	DHCP reset), you  should  make
	      use of one or more of the	--persist options to ensure that Open-
	      VPN doesn't need to execute any privileged operations  in	 order
	      to  restart (such	as re-reading key files	or running ifconfig on
	      the TUN device).

       --group group
	      Similar to the --user option, this option	changes	the  group  ID
	      of the OpenVPN process to	group after initialization.

       --cd dir
	      Change  directory	to dir prior to	reading	any files such as con-
	      figuration files,	key files, scripts, etc.   dir	should	be  an
	      absolute path, with a leading "/", and without any references to
	      the current directory such as "."	or "..".

	      This option is useful when you are running OpenVPN  in  --daemon
	      mode,  and  you  want to consolidate all of your OpenVPN control
	      files in one location.

       --chroot	dir
	      Chroot to	dir after initialization.  --chroot essentially	 rede-
	      fines  dir  as  being the	top level directory tree (/).  OpenVPN
	      will therefore be	unable to access any files outside this	 tree.
	      This can be desirable from a security standpoint.

	      Since  the  chroot  operation is delayed until after initializa-
	      tion, most OpenVPN options that reference	files will operate  in
	      a	pre-chroot context.

	      In  many	cases,	the dir	parameter can point to an empty	direc-
	      tory, however complications can result when scripts or  restarts
	      are executed after the chroot operation.

	      Note:  The  SSL  library	will  probably need /dev/urandom to be
	      available	inside the chroot directory dir.  This is because  SSL
	      libraries	 occasionally  need  to	 collect  fresh	random.	 Newer
	      linux kernels and	some BSDs implement a  getrandom()  or	geten-
	      tropy()  syscall	that  removes  the need	for /dev/urandom to be

       --setcon	context
	      Apply SELinux context  after  initialization.  This  essentially
	      provides	the  ability to	restrict OpenVPN's rights to only net-
	      work I/O operations, thanks to SELinux. This goes	 further  than
	      --user  and  --chroot in that those two, while being great secu-
	      rity features, unfortunately do not  protect  against  privilege
	      escalation  by exploitation of a vulnerable system call. You can
	      of course	combine	all three, but please note that	 since	setcon
	      requires	access to /proc	you will have to provide it inside the
	      chroot directory (e.g. with mount	--bind).

	      Since the	setcon operation is delayed  until  after  initializa-
	      tion,  OpenVPN  can be restricted	to just	network-related	system
	      calls, whereas by	applying the context before startup  (such  as
	      the  OpenVPN one provided	in the SELinux Reference Policies) you
	      will have	to allow many things required only during  initializa-

	      Like  with  chroot,  complications  can  result  when scripts or
	      restarts are executed after the setcon operation,	which  is  why
	      you  should  really  consider using the --persist-key and	--per-
	      sist-tun options.

       --daemon	[progname]
	      Become a daemon after  all  initialization  functions  are  com-
	      pleted.	This option will cause all message and error output to
	      be sent to the syslog file (such as  /var/log/messages),	except
	      for  the	output of scripts and ifconfig commands, which will go
	      to /dev/null unless otherwise redirected.	 The syslog  redirect-
	      ion  occurs  immediately at the point that --daemon is parsed on
	      the command line even  though  the  daemonization	 point	occurs
	      later.   If  one	of  the	 --log	options	 is  present,  it will
	      supercede	syslog redirection.

	      The optional progname parameter will cause OpenVPN to report its
	      program name to the system logger	as progname.  This can be use-
	      ful in linking OpenVPN messages in the syslog file with specific
	      tunnels.	When unspecified, progname defaults to "openvpn".

	      When  OpenVPN  is	 run  with the --daemon	option,	it will	try to
	      delay daemonization until	the majority of	 initialization	 func-
	      tions which are capable of generating fatal errors are complete.
	      This means that initialization scripts can test the return  sta-
	      tus  of  the openvpn command for a fairly	reliable indication of
	      whether the command has correctly	initialized  and  entered  the
	      packet forwarding	event loop.

	      In  OpenVPN,  the	vast majority of errors	which occur after ini-
	      tialization are non-fatal.

	      Note: as soon as OpenVPN has daemonized,	it  can	 not  ask  for
	      usernames,  passwords,  or  key  pass phrases anymore.  This has
	      certain consequences, namely  that  using	 a  password-protected
	      private  key  will  fail	unless the --askpass option is used to
	      tell OpenVPN to ask for the pass phrase (this requirement	is new
	      in  2.3.7,  and is a consequence of calling daemon() before ini-
	      tializing	the crypto layer).

	      Further, using --daemon together with --auth-user-pass  (entered
	      on  console) and --auth-nocache will fail	as soon	as key renego-
	      tiation (and reauthentication) occurs.

       --syslog	[progname]
	      Direct log output	to system logger, but do not become a  daemon.
	      See --daemon directive above for description of progname parame-

	      Output errors to stderr instead of stdout	unless log  output  is
	      redirected by one	of the --log options.

	      Set the TOS field	of the tunnel packet to	what the payload's TOS

       --inetd [wait|nowait] [progname]
	      Use this option when OpenVPN is being  run  from	the  inetd  or
	      xinetd(8)	server.

	      The  wait/nowait	option	must  match  what  is specified	in the
	      inetd/xinetd config file.	 The nowait mode can only be used with
	      --proto  tcp-server.   The default is wait.  The nowait mode can
	      be used to instantiate the  OpenVPN  daemon  as  a  classic  TCP
	      server,  where client connection requests	are serviced on	a sin-
	      gle port number.	For additional information  on	this  kind  of
	      configuration,	 see	the    OpenVPN	  FAQ:	  http://open-

	      This option precludes the	use of --daemon, --local, or --remote.
	      Note that	this option causes message and error output to be han-
	      dled in the same way as the --daemon option.  The	optional prog-
	      name parameter is	also handled exactly as	in --daemon.

	      Also note	that in	wait mode, each	OpenVPN	tunnel requires	a sep-
	      arate TCP/UDP port and a separate	inetd or  xinetd  entry.   See
	      the  OpenVPN  1.x	 HOWTO	for  an	 example on using OpenVPN with

       --log file
	      Output logging  messages	to  file,  including  output  to  std-
	      out/stderr  which	 is  generated	by  called  scripts.   If file
	      already exists it	will be	truncated.  This option	 takes	effect
	      immediately  when	 it  is	 parsed	 in  the command line and will
	      supercede	syslog output if --daemon or --inetd  is  also	speci-
	      fied.   This  option  is persistent over the entire course of an
	      OpenVPN instantiation and	will not be reset by SIGHUP,  SIGUSR1,
	      or --ping-restart.

	      Note that	on Windows, when OpenVPN is started as a service, log-
	      ging occurs by default without the need to specify this  option.

       --log-append file
	      Append  logging  messages	 to  file.  If file does not exist, it
	      will be created.	This option behaves exactly like --log	except
	      that it appends to rather	than truncating	the log	file.

	      Avoid  writing timestamps	to log messages, even when they	other-
	      wise would be prepended. In particular, this applies to log mes-
	      sages sent to stdout.

       --writepid file
	      Write OpenVPN's main process ID to file.

       --nice n
	      Change  process priority after initialization ( n	greater	than 0
	      is lower priority, n less	than zero is higher priority).

	      (Experimental) Optimize TUN/TAP/UDP I/O  writes  by  avoiding  a
	      call  to	poll/epoll/select  prior  to the write operation.  The
	      purpose of such a	call would normally  be	 to  block  until  the
	      device or	socket is ready	to accept the write.  Such blocking is
	      unnecessary on some platforms which don't	support	write blocking
	      on UDP sockets or	TUN/TAP	devices.  In such cases, one can opti-
	      mize the event loop  by  avoiding	 the  poll/epoll/select	 call,
	      improving	CPU efficiency by 5% to	10%.

	      This  option  can	 only  be  used	 on  non-Windows systems, when
	      --proto udp is specified,	and when --shaper is NOT specified.

	      Configure	a multi-homed UDP server.  This	 option	 needs	to  be
	      used  when  a server has more than one IP	address	(e.g. multiple
	      interfaces, or secondary IP addresses), and is not using --local
	      to force binding to one specific address only.  This option will
	      add some extra lookups to	the packet path	to ensure that the UDP
	      reply  packets  are always sent from the address that the	client
	      is talking to. This is not supported on all  platforms,  and  it
	      adds more	processing, so it's not	enabled	by default.

	      Note: this option	is only	relevant for UDP servers.

	      Note  2:	if  you	 do  an	 IPv6+IPv4  dual-stack bind on a Linux
	      machine  with  multiple  IPv4  address,  connections   to	  IPv4
	      addresses	 will  not  work  right	on kernels before 3.15,	due to
	      missing kernel support for the IPv4-mapped case (some  distribu-
	      tions have ported	this to	earlier	kernel versions, though).

       --echo [parms...]
	      Echo parms to log	output.

	      Designed	to  be used to send messages to	a controlling applica-
	      tion which is receiving the OpenVPN log output.

       --remap-usr1 signal
	      Control whether internally or externally generated SIGUSR1  sig-
	      nals  are	 remapped to SIGHUP (restart without persisting	state)
	      or SIGTERM (exit).

	      signal can be set	to "SIGHUP"  or	 "SIGTERM".   By  default,  no
	      remapping	occurs.

       --verb n
	      Set  output  verbosity  to  n (default=1).  Each level shows all
	      info from	the previous levels.  Level 3 is  recommended  if  you
	      want a good summary of what's happening without being swamped by

	      0	-- No output except fatal errors.
	      1	to 4 --	Normal usage range.
	      5	-- Output R and	W characters to	the console  for  each	packet
	      read and write, uppercase	is used	for TCP/UDP packets and	lower-
	      case is used for TUN/TAP packets.
	      6	to 11 -- Debug	info  range  (see  errlevel.h  for  additional
	      information on debug levels).

       --status	file [n]
	      Write operational	status to file every n seconds.

	      Status  can  also	 be written to the syslog by sending a SIGUSR2

       --status-version	[n]
	      Choose the status	file format version number.  Currently	n  can
	      be 1, 2, or 3 and	defaults to 1.

       --mute n
	      Log  at  most n consecutive messages in the same category.  This
	      is useful	to limit repetitive logging of similar message	types.

       --comp-lzo [mode]
	      Use  fast	LZO compression	-- may add up to 1 byte	per packet for
	      incompressible data.  mode may be	 "yes",	 "no",	or  "adaptive"

	      In  a server mode	setup, it is possible to selectively turn com-
	      pression on or off for individual	clients.

	      First, make sure the client-side config file  enables  selective
	      compression by having at least one --comp-lzo directive, such as
	      --comp-lzo no.  This will	turn off compression by	 default,  but
	      allow  a	future	directive  push	from the server	to dynamically
	      change the on/off/adaptive setting.

	      Next in a	--client-config-dir file, specify the compression set-
	      ting for the client, for example:

		  comp-lzo yes
		  push "comp-lzo yes"

	      The  first line sets the comp-lzo	setting	for the	server side of
	      the link,	the second sets	the client side.

	      When used	in conjunction with --comp-lzo,	this option will  dis-
	      able  OpenVPN's adaptive compression algorithm.  Normally, adap-
	      tive compression is enabled with --comp-lzo.

	      Adaptive compression tries to optimize the case where  you  have
	      compression  enabled,  but  you are sending predominantly	incom-
	      pressible	(or pre-compressed) packets over the tunnel,  such  as
	      an  FTP  or  rsync  transfer  of a large,	compressed file.  With
	      adaptive compression, OpenVPN will periodically sample the  com-
	      pression	process	 to measure its	efficiency.  If	the data being
	      sent over	the tunnel  is	already	 compressed,  the  compression
	      efficiency  will be very low, triggering openvpn to disable com-
	      pression for a period of time until the next re-sample test.

       --management IP port [pw-file]
	      Enable a TCP server on IP:port to	handle daemon management func-
	      tions.   pw-file,	 if specified, is a password file (password on
	      first line) or "stdin" to	prompt from standard input.  The pass-
	      word  provided will set the password which TCP clients will need
	      to provide in order to access management functions.

	      The management interface	can  also  listen  on  a  unix	domain
	      socket,  for  those  platforms  that  support it.	 To use	a unix
	      domain socket, specify the unix socket pathname in place	of  IP
	      and set port to 'unix'.  While the default behavior is to	create
	      a	unix domain socket that	may be connected to  by	 any  process,
	      the   --management-client-user   and   --management-client-group
	      directives can be	used to	restrict access.

	      The management interface provides	a special mode where  the  TCP
	      management  link	can operate over the tunnel itself.  To	enable
	      this mode, set IP	= "tunnel".  Tunnel mode will cause  the  man-
	      agement  interface  to  listen for a TCP connection on the local
	      VPN address of the TUN/TAP interface.

	      While the	management port	is designed for	 programmatic  control
	      of  OpenVPN  by  other applications, it is possible to telnet to
	      the port,	using a	telnet client in "raw" mode.  Once  connected,
	      type "help" for a	list of	commands.

	      For  detailed documentation on the management interface, see the
	      management-notes.txt file	in the management folder of the	 Open-
	      VPN source distribution.

	      It  is  strongly recommended that	IP be set to (local-
	      host) to restrict	accessibility  of  the	management  server  to
	      local clients.

	      Management interface will	connect	as a TCP/unix domain client to
	      IP:port specified	by --management	rather than listen  as	a  TCP
	      server or	on a unix domain socket.

	      If  the client connection	fails to connect or is disconnected, a
	      SIGTERM signal will be generated causing OpenVPN to quit.

	      Query  management	 channel  for	private	  key	password   and
	      --auth-user-pass	username/password.   Only query	the management
	      channel for inputs which ordinarily would	have been queried from
	      the console.

	      Query management channel for proxy server	information for	a spe-
	      cific --remote (client-only).

	      Allow  management	 interface  to	override  --remote  directives
	      (client-only).	--management-external-key   Allows  usage  for
	      external private key file	instead	of --key option	(client-only).

	      Make  OpenVPN  forget  passwords when management session discon-

	      This directive does not affect the  --http-proxy	username/pass-
	      word.  It	is always cached.

	      Start OpenVPN in a hibernating state, until a client of the man-
	      agement interface	explicitly starts it  with  the	 hold  release

	      Send  SIGUSR1  signal  to	 OpenVPN if management session discon-
	      nects.  This is useful when you wish to  disconnect  an  OpenVPN
	      session  on  user	logoff.	For --management-client	this option is
	      not needed since a disconnect will always	generate a SIGTERM.

       --management-log-cache n
	      Cache the	most recent n lines of log file	history	for  usage  by
	      the management channel.

	      Report tunnel up/down events to management interface.

	      Gives  management	interface client the responsibility to authen-
	      ticate clients after their client	certificate has	been verified.
	      See  management-notes.txt	 in  OpenVPN distribution for detailed

	      Management interface clients must	specify	a packet  filter  file
	      for each connecting client.  See management-notes.txt in OpenVPN
	      distribution for detailed	notes.

       --management-client-user	u
	      When the management interface is	listening  on  a  unix	domain
	      socket, only allow connections from user u.

       --management-client-group g
	      When  the	 management  interface	is  listening on a unix	domain
	      socket, only allow connections from group	g.

       --plugin	module-pathname	[init-string]
	      Load plug-in module from the file	module-pathname, passing init-
	      string  as  an  argument	to the module initialization function.
	      Multiple plugin modules may be loaded into one OpenVPN  process.

	      For  more	information and	examples on how	to build OpenVPN plug-
	      in modules, see the README file in  the  plugin  folder  of  the
	      OpenVPN source distribution.

	      If you are using an RPM install of OpenVPN, see /usr/share/open-
	      vpn/plugin.  The documentation is	in doc and the	actual	plugin
	      modules are in lib.

	      Multiple plugin modules can be cascaded, and modules can be used
	      in tandem	with scripts.  The modules will	be called  by  OpenVPN
	      in the order that	they are declared in the config	file.  If both
	      a	plugin and script are configured for the  same	callback,  the
	      script  will  be	called	last.	If the return code of the mod-
	      ule/script controls an authentication function (such as tls-ver-
	      ify,  auth-user-pass-verify, or client-connect), then every mod-
	      ule and script must return success (0) in	order for the  connec-
	      tion to be authenticated.

   Server Mode
       Starting	 with  OpenVPN 2.0, a multi-client TCP/UDP server mode is sup-
       ported, and can be enabled with the --mode server  option.   In	server
       mode,  OpenVPN will listen on a single port for incoming	client connec-
       tions.  All client connections will be routed through a single  tun  or
       tap  interface.	 This  mode  is	designed for scalability and should be
       able to support hundreds	or even	thousands of clients  on  sufficiently
       fast hardware.  SSL/TLS authentication must be used in this mode.

       --server	network	netmask	['nopool']
	      A	 helper	 directive  designed  to simplify the configuration of
	      OpenVPN's	server mode.  This directive will set  up  an  OpenVPN
	      server which will	allocate addresses to clients out of the given
	      network/netmask.	The server itself will take the	 ".1"  address
	      of  the given network for	use as the server-side endpoint	of the
	      local TUN/TAP interface.

	      For example, --server expands as follows:

		   mode	server
		   push	"topology [topology]"

		   if dev tun AND (topology == net30 OR	topology == p2p):
		     if	!nopool:
		     if	client-to-client:
		       push "route"
		     else if topology == net30:
		       push "route"

		   if dev tap OR (dev tun AND topology == subnet):
		     if	!nopool:
		     push "route-gateway"
		     if	route-gateway unset:

	      Don't   use   --server   if  you	are  ethernet  bridging.   Use
	      --server-bridge instead.

       --server-bridge gateway netmask pool-start-IP pool-end-IP

       --server-bridge ['nogw']

	      A	helper directive similar to --server which is designed to sim-
	      plify  the  configuration	 of  OpenVPN's server mode in ethernet
	      bridging configurations.

	      If --server-bridge is  used  without  any	 parameters,  it  will
	      enable  a	DHCP-proxy mode, where connecting OpenVPN clients will
	      receive an IP address for	their TAP adapter from the DHCP	server
	      running  on the OpenVPN server-side LAN.	Note that only clients
	      that support the binding of a DHCP client	with the  TAP  adapter
	      (such as Windows)	can support this mode.	The optional nogw flag
	      (advanced) indicates that	 gateway  information  should  not  be
	      pushed to	the client.

	      To  configure  ethernet  bridging,  you must first use your OS's
	      bridging capability to bridge the	TAP interface with the	ether-
	      net  NIC interface.  For example,	on Linux this is done with the
	      brctl tool, and with Windows XP it is done in the	 Network  Con-
	      nections	Panel  by  selecting the ethernet and TAP adapters and
	      right-clicking on	"Bridge	Connections".

	      Next you you must	manually set  the  IP/netmask  on  the	bridge
	      interface.     The    gateway    and   netmask   parameters   to
	      --server-bridge can be set  to  either  the  IP/netmask  of  the
	      bridge  interface,  or  the  IP/netmask  of  the	default	 gate-
	      way/router on the	bridged	subnet.

	      Finally, set aside a IP range in the bridged subnet, denoted  by
	      pool-start-IP  and  pool-end-IP, for OpenVPN to allocate to con-
	      necting clients.

	      For example,  server-bridge expands as follows:

		  mode server

		  push "route-gateway"

	      In another example, --server-bridge (without parameters) expands
	      as follows:

		  mode server

		  push "route-gateway dhcp"

	      Or --server-bridge nogw expands as follows:

		  mode server

       --push option
	      Push a config file option	back to	the client for	remote	execu-
	      tion.   Note that	option must be enclosed	in double quotes ("").
	      The client must specify --pull in	its config file.  The  set  of
	      options  which  can be pushed is limited by both feasibility and
	      security.	 Some  options	such  as  those	 which	would  execute
	      scripts are banned, since	they would effectively allow a compro-
	      mised server to execute arbitrary	code  on  the  client.	 Other
	      options  such  as	TLS or MTU parameters cannot be	pushed because
	      the client needs to know	them  before  the  connection  to  the
	      server can be initiated.

	      This is a	partial	list of	options	which can currently be pushed:
	      --route,	--route-gateway,  --route-delay,   --redirect-gateway,
	      --ip-win32,   --dhcp-option,  --inactive,	 --ping,  --ping-exit,
	      --ping-restart, --setenv,	--persist-key, --persist-tun,  --echo,
	      --comp-lzo, --socket-flags, --sndbuf, --rcvbuf

	      Don't  inherit  the  global  push	 list  for  a  specific	client
	      instance.	 Specify this option in	a client-specific context such
	      as  with	a --client-config-dir configuration file.  This	option
	      will ignore --push options at the	global config file level.

	      Push additional information about	the  client  to	 server.   The
	      additional information consists of the following data:

	      IV_VER=<version> -- the client OpenVPN version

	      IV_PLAT=[linux|solaris|openbsd|mac|netbsd|freebsd|win]   --  the
	      client OS	platform

	      IV_HWADDR=<mac address> -- the MAC address  of  clients  default

	      IV_LZO_STUB=1 -- if client was built with	LZO stub capability

	      UV_<name>=<value>	 --  client  environment variables whose names
	      start with "UV_"

	      Disable a	particular client (based on the	common name) from con-
	      necting.	 Don't	use this option	to disable a client due	to key
	      or password compromise.  Use a CRL (certificate revocation list)
	      instead (see the --crl-verify option).

	      This  option must	be associated with a specific client instance,
	      which means that	it  must  be  specified	 either	 in  a	client
	      instance	config	file  using --client-config-dir	or dynamically
	      generated	using a	--client-connect script.

       --ifconfig-pool start-IP	end-IP [netmask]
	      Set aside	a pool of subnets to be	dynamically allocated to  con-
	      necting  clients,	 similar to a DHCP server.  For	tun-style tun-
	      nels, each client	will be	given a	/30 subnet (for	interoperabil-
	      ity  with	 Windows  clients).  For tap-style tunnels, individual
	      addresses	will be	allocated, and the optional netmask  parameter
	      will also	be pushed to clients.

       --ifconfig-pool-persist file [seconds]
	      Persist/unpersist	 ifconfig-pool data to file, at	seconds	inter-
	      vals (default=600), as well as on	program	startup	and  shutdown.

	      The  goal	 of  this option is to provide a long-term association
	      between clients (denoted by their	common name) and  the  virtual
	      IP address assigned to them from the ifconfig-pool.  Maintaining
	      a	long-term association is good for clients  because  it	allows
	      them to effectively use the --persist-tun	option.

	      file  is	a  comma-delimited  ASCII  file, formatted as <Common-

	      If seconds = 0, file will	be treated as read-only.  This is use-
	      ful if you would like to treat file as a configuration file.

	      Note  that  the  entries	in this	file are treated by OpenVPN as
	      suggestions only,	based on past associations  between  a	common
	      name  and	IP address.  They do not guarantee that	the given com-
	      mon name will always receive the given IP	address.  If you  want
	      guaranteed assignment, use --ifconfig-push

	      Modifies	the  --ifconfig-pool  directive	to allocate individual
	      TUN interface addresses for clients  rather  than	 /30  subnets.
	      NOTE:  This option is incompatible with Windows clients.

	      This  option is deprecated, and should be	replaced with --topol-
	      ogy p2p which is functionally equivalent.

       --ifconfig-push local remote-netmask [alias]
	      Push virtual IP endpoints	 for  client  tunnel,  overriding  the
	      --ifconfig-pool dynamic allocation.

	      The parameters local and remote-netmask are set according	to the
	      --ifconfig directive which you want to  execute  on  the	client
	      machine  to  configure  the remote end of	the tunnel.  Note that
	      the parameters local and remote-netmask are from the perspective
	      of  the  client,	not  the server.  They may be DNS names	rather
	      than IP addresses, in which case they will be  resolved  on  the
	      server at	the time of client connection.

	      The  optional  alias  parameter  may  be used in cases where NAT
	      causes the client	view of	its local endpoint to differ from  the
	      server  view.   In  this case local/remote-netmask will refer to
	      the server view while alias/remote-netmask  will	refer  to  the
	      client view.

	      This  option must	be associated with a specific client instance,
	      which means that	it  must  be  specified	 either	 in  a	client
	      instance	config	file  using --client-config-dir	or dynamically
	      generated	using a	--client-connect script.

	      Remember also to include a --route directive in the main OpenVPN
	      config  file  which encloses local, so that the kernel will know
	      to route it to the server's TUN/TAP interface.

	      OpenVPN's	internal client	IP address selection  algorithm	 works
	      as follows:

	      1	 --  Use  --client-connect script generated file for static IP
	      (first choice).
	      2	-- Use --client-config-dir file	for static IP (next choice).
	      3	 --  Use  --ifconfig-pool  allocation  for  dynamic  IP	 (last

       --iroute	network	[netmask]
	      Generate	an  internal  route  to	a specific client. The netmask
	      parameter, if omitted, defaults to

	      This directive can be used to route  a  fixed  subnet  from  the
	      server to	a particular client, regardless	of where the client is
	      connecting from.	Remember that you must also add	the  route  to
	      the  system  routing table as well (such as by using the --route
	      directive).  The reason why two routes are needed	 is  that  the
	      --route  directive routes	the packet from	the kernel to OpenVPN.
	      Once in OpenVPN, the --iroute directive routes to	 the  specific

	      This option must be specified either in a	client instance	config
	      file using --client-config-dir or	dynamically generated using  a
	      --client-connect script.

	      The  --iroute  directive	also has an important interaction with
	      --push "route ...".  --iroute essentially	defines	a subnet which
	      is  owned	 by  a particular client (we will call this client A).
	      If you would like	other clients to be able to reach A's  subnet,
	      you can use --push "route	..."  together with --client-to-client
	      to effect	this.  In order	for all	clients	 to  see  A's  subnet,
	      OpenVPN  must push this route to all clients EXCEPT for A, since
	      the subnet is already owned by A.	 OpenVPN accomplishes this  by
	      not  not	pushing	 a  route to a client if it matches one	of the
	      client's iroutes.

	      Because the OpenVPN server mode handles multiple clients through
	      a	 single	tun or tap interface, it is effectively	a router.  The
	      --client-to-client  flag	tells  OpenVPN	to  internally	 route
	      client-to-client	traffic	 rather	than pushing all client-origi-
	      nating traffic to	the TUN/TAP interface.

	      When this	option is used,	 each  client  will  "see"  the	 other
	      clients  which  are currently connected.	Otherwise, each	client
	      will only	see the	server.	 Don't use this	option if you want  to
	      firewall tunnel traffic using custom, per-client rules.

	      Allow multiple clients with the same common name to concurrently
	      connect.	In the absence of this option, OpenVPN will disconnect
	      a	 client	 instance  upon	 connection of a new client having the
	      same common name.

       --client-connect	cmd
	      Run command cmd on client	connection.

	      cmd consists of  a  path	to  script  (or	 executable  program),
	      optionally  followed by arguments. The path and arguments	may be
	      single- or double-quoted and/or escaped using a  backslash,  and
	      should be	separated by one or more spaces.

	      The  command  is	passed	the  common name and IP	address	of the
	      just-authenticated client	as environmental variables (see	 envi-
	      ronmental	 variable  section below).  The	command	is also	passed
	      the pathname of a	freshly	created	temporary  file	 as  the  last
	      argument	(after any arguments specified in cmd ), to be used by
	      the command to pass dynamically generated	config file directives
	      back to OpenVPN.

	      If  the  script  wants  to  generate a dynamic config file to be
	      applied on the server when the client connects, it should	 write
	      it to the	file named by the last argument.

	      See  the	--client-config-dir option below for options which can
	      be legally used in a dynamically generated config	file.

	      Note that	the return value of script is significant.  If	script
	      returns  a non-zero error	status,	it will	cause the client to be

       --client-disconnect cmd
	      Like --client-connect but	called on  client  instance  shutdown.
	      Will  not	be called unless the --client-connect script and plug-
	      ins (if defined) were previously called on  this	instance  with
	      successful (0) status returns.

	      The exception to this rule is if the --client-disconnect command
	      or plugins are cascaded, and at least one	 client-connect	 func-
	      tion  succeeded, then ALL	of the client-disconnect functions for
	      scripts and plugins will be called  on  client  instance	object
	      deletion,	even in	cases where some of the	related	client-connect
	      functions	returned an error status.

	      The --client-disconnect command is passed	the same  pathname  as
	      the corresponding	--client-connect command as its	last argument.
	      (after any arguments specified in	cmd ).

       --client-config-dir dir
	      Specify a	directory dir for custom client	config files.  After a
	      connecting  client  has been authenticated, OpenVPN will look in
	      this directory for a file	having the same	name as	 the  client's
	      X509  common name.  If a matching	file exists, it	will be	opened
	      and parsed for client-specific  configuration  options.	If  no
	      matching	file  is  found,  OpenVPN will instead try to open and
	      parse a default file called "DEFAULT", which may be provided but
	      is not required. Note that the configuration files must be read-
	      able by the OpenVPN process after	it has dropped it's root priv-

	      This  file  can  specify	a  fixed IP address for	a given	client
	      using --ifconfig-push, as	well as	fixed  subnets	owned  by  the
	      client using --iroute.

	      One  of  the  useful properties of this option is	that it	allows
	      client configuration files to be conveniently  created,  edited,
	      or  removed while	the server is live, without needing to restart
	      the server.

	      The following options are	legal in  a  client-specific  context:
	      --push, --push-reset, --iroute, --ifconfig-push, and --config.

	      Require,	as  a  condition  of authentication, that a connecting
	      client has a --client-config-dir file.

       --tmp-dir dir
	      Specify a	directory dir for  temporary  files.   This  directory
	      will be used by openvpn processes	and script to communicate tem-
	      porary data with openvpn main process. Note that	the  directory
	      must  be	writable  by  the OpenVPN process after	it has dropped
	      it's root	privileges.

	      This directory will be used by in	the following cases:

	      *	--client-connect scripts to dynamically	 generate  client-spe-
	      cific configuration files.

	      *	 OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY  plugin  hook  to	return
	      success/failure via auth_control_file when using	deferred  auth

	      *	 OPENVPN_PLUGIN_ENABLE_PF  plugin hook to pass filtering rules
	      via pf_file

       --hash-size r v
	      Set the size of the real address hash table to r and the virtual
	      address  table  to  v.  By default, both tables are sized	at 256

       --bcast-buffers n
	      Allocate n buffers for broadcast datagrams (default=256).

       --tcp-queue-limit n
	      Maximum number of	output packets queued before TCP (default=64).

	      When OpenVPN is tunneling	data from a TUN/TAP device to a	remote
	      client over a TCP	connection, it is possible  that  the  TUN/TAP
	      device  might produce data at a faster rate than the TCP connec-
	      tion can support.	 When the  number  of  output  packets	queued
	      before  sending to the TCP socket	reaches	this limit for a given
	      client connection, OpenVPN will start to drop  outgoing  packets
	      directed at this client.

	      This  macro  sets	 the  TCP_NODELAY socket flag on the server as
	      well as pushes it	to connecting clients.	The  TCP_NODELAY  flag
	      disables	the  Nagle algorithm on	TCP sockets causing packets to
	      be transmitted immediately with low latency, rather than waiting
	      a	 short	period	of  time in order to aggregate several packets
	      into a larger containing packet.	In VPN applications over  TCP,
	      TCP_NODELAY is generally a good latency optimization.

	      The macro	expands	as follows:

		   if mode server:
		     socket-flags TCP_NODELAY
		     push "socket-flags	TCP_NODELAY"

       --max-clients n
	      Limit server to a	maximum	of n concurrent	clients.

       --max-routes-per-client n
	      Allow  a	maximum	of n internal routes per client	(default=256).
	      This is designed to help contain DoS attacks where an  authenti-
	      cated  client  floods  the server	with packets appearing to come
	      from many	unique MAC addresses, forcing the  server  to  deplete
	      virtual  memory  as  its	internal  routing table	expands.  This
	      directive	can be used in a --client-config-dir file or auto-gen-
	      erated by	a --client-connect script to override the global value
	      for a particular client.

	      Note that	this directive affects OpenVPN's internal routing  ta-
	      ble, not the kernel routing table.

       --stale-routes-check n [t]
	      Remove  routes haven't had activity for n	seconds	(i.e. the age-
	      ing time).

	      This check is ran	every t	seconds	(i.e. check interval).

	      If t is not present it defaults to n

	      This option helps	to keep	the dynamic routing table small.   See
	      also --max-routes-per-client

       --connect-freq n	sec
	      Allow  a	maximum	 of  n	new  connections  per sec seconds from
	      clients.	This is	designed to contain DoS	 attacks  which	 flood
	      the  server  with	 connection  requests using certificates which
	      will ultimately fail to authenticate.

	      This is an imperfect solution however, because  in  a  real  DoS
	      scenario,	legitimate connections might also be refused.

	      For  the best protection against DoS attacks in server mode, use
	      --proto udp and --tls-auth.

       --learn-address cmd
	      Run command cmd to validate client virtual addresses or  routes.

	      cmd  consists  of	 a  path  to  script  (or executable program),
	      optionally followed by arguments.	The path and arguments may  be
	      single-  or  double-quoted and/or	escaped	using a	backslash, and
	      should be	separated by one or more spaces.

	      Three arguments will be appended to any arguments	in cmd as fol-

	      [1]  operation  -- "add",	"update", or "delete" based on whether
	      or not the address is being added	to, modified, or deleted  from
	      OpenVPN's	internal routing table.
	      [2] address -- The address being learned or unlearned.  This can
	      be an IPv4 address such as "", an IPv4 subnet  such
	      as "", or an ethernet MAC address (when --dev tap
	      is being used) such as "00:FF:01:02:03:04".
	      [3] common name -- The common name on the	certificate associated
	      with  the	client linked to this address.	Only present for "add"
	      or "update" operations, not "delete".

	      On "add" or "update" methods, if the script  returns  a  failure
	      code  (non-zero),	 OpenVPN  will reject the address and will not
	      modify its internal routing table.

	      Normally,	the cmd	script will use	the information	provided above
	      to  set  appropriate  firewall entries on	the VPN	TUN/TAP	inter-
	      face.  Since OpenVPN provides the	association between virtual IP
	      or  MAC  address	and the	client's authenticated common name, it
	      allows a user-defined script to configure	firewall access	 poli-
	      cies  with regard	to the client's	high-level common name,	rather
	      than the low level client	virtual	addresses.

       --auth-user-pass-verify cmd method
	      Require the client to provide a username/password	 (possibly  in
	      addition to a client certificate)	for authentication.

	      OpenVPN  will  run command cmd to	validate the username/password
	      provided by the client.

	      cmd consists of  a  path	to  script  (or	 executable  program),
	      optionally  followed by arguments. The path and arguments	may be
	      single- or double-quoted and/or escaped using a  backslash,  and
	      should be	separated by one or more spaces.

	      If method	is set to "via-env", OpenVPN will call script with the
	      environmental variables username and password set	to  the	 user-
	      name/password  strings  provided	by  the	client.	 Be aware that
	      this method is insecure on some platforms	which make  the	 envi-
	      ronment of a process publicly visible to other unprivileged pro-

	      If method	is set to "via-file", OpenVPN will write the  username
	      and  password  to	 the first two lines of	a temporary file.  The
	      filename will be passed as an argument to	script,	and  the  file
	      will  be	automatically  deleted	by  OpenVPN  after  the	script
	      returns.	The location of	the temporary file  is	controlled  by
	      the  --tmp-dir option, and will default to the current directory
	      if unspecified.  For security, consider setting --tmp-dir	 to  a
	      volatile	storage	medium such as /dev/shm	(if available) to pre-
	      vent the username/password file from touching the	hard drive.

	      The script should	examine	the username and password, returning a
	      success  exit code (0) if	the client's authentication request is
	      to be accepted, or a failure code	(1) to reject the client.

	      This directive is	designed to enable  a  plugin-style  interface
	      for extending OpenVPN's authentication capabilities.

	      To  protect  against a client passing a maliciously formed user-
	      name or password string, the username string must	 consist  only
	      of  these	 characters: alphanumeric, underbar ('_'), dash	('-'),
	      dot ('.'), or at ('@').  The password string can consist of  any
	      printable	 characters  except for	CR or LF.  Any illegal charac-
	      ters in either the username or password string will be converted
	      to underbar ('_').

	      Care must	be taken by any	user-defined scripts to	avoid creating
	      a	security vulnerability in the way that these strings are  han-
	      dled.   Never use	these strings in such a	way that they might be
	      escaped or evaluated by a	shell interpreter.

	      For a sample script that performs	PAM authentication,  see  sam-
	      ple-scripts/ in the OpenVPN source distribution.

	      Clients  that  connect  with  options that are incompatible with
	      those of the server will be disconnected.

	      Options that will	be compared  for  compatibility	 include  dev-
	      type,  link-mtu,	tun-mtu,  proto, tun-ipv6, ifconfig, comp-lzo,
	      fragment,	keydir,	cipher,	auth, keysize, secret, no-replay,  no-
	      iv, tls-auth, key-method,	tls-server, and	tls-client.

	      This option requires that	--disable-occ NOT be used.

	      Allow  connections  by  clients  that  do	 not  specify  a user-
	      name/password.  Normally,	when --auth-user-pass-verify or	--man-
	      agement-client-auth  is  specified  (or an authentication	plugin
	      module), the  OpenVPN  server  daemon  will  require  connecting
	      clients  to  specify a username and password.  This option makes
	      the submission of	a username/password by clients optional, pass-
	      ing  the	responsibility to the user-defined authentication mod-
	      ule/script to accept or deny the client based on	other  factors
	      (such  as	 the  setting  of X509 certificate fields).  When this
	      option is	used, and a connecting client does not submit a	 user-
	      name/password,  the  user-defined	 authentication	 module/script
	      will see the username and	password as being set to empty strings
	      ("").   The  authentication  module/script  MUST	have  logic to
	      detect this condition and	respond	accordingly.

	      Don't require client certificate,	client will authenticate using
	      username/password	 only.	 Be aware that using this directive is
	      less secure than requiring certificates from all clients.

	      If you use this directive, the entire responsibility of  authen-
	      tication	will  rest  on your --auth-user-pass-verify script, so
	      keep in mind that	bugs in	your script could potentially  compro-
	      mise the security	of your	VPN.

	      If  you  don't  use  this	 directive,  but  you  also specify an
	      --auth-user-pass-verify script, then OpenVPN will	perform	double
	      authentication.	The  client  certificate  verification AND the
	      --auth-user-pass-verify script will need to succeed in order for
	      a	client to be authenticated and accepted	onto the VPN.

	      For  --auth-user-pass-verify  authentication,  use the authenti-
	      cated username as	the common name, rather	than the  common  name
	      from the client cert.

       --compat-names [no-remapping] (DEPRECATED)
	      Until  OpenVPN  v2.3  the	format of the X.509 Subject fields was
	      formatted	like this:

	      /C=US/L=Somewhere/CN=John	Doe/

	      In addition the old behaviour was	to remap any  character	 other
	      than  alphanumeric, underscore ('_'), dash ('-'),	dot ('.'), and
	      slash ('/') to underscore	('_').	The X.509  Subject  string  as
	      returned	by  the	tls_id environmental variable, could addition-
	      ally contain colon (':') or equal	('=').

	      When using the --compat-names option, this  old  formatting  and
	      remapping	 will be re-enabled again.  This is purely implemented
	      for compatibility	reasons	when using older plug-ins  or  scripts
	      which does not handle the	new formatting or UTF-8	characters.

	      In  OpenVPN  v2.3	 the formatting	of these fields	changed	into a
	      more standardised	format.	 It now	looks like:

	      C=US, L=Somewhere, CN=John Doe,

	      The new default format in	OpenVPN	v2.3  also  does  not  do  the
	      character	 remapping  which  happened  earlier.  This new	format
	      enables proper support for UTF-8 characters  in  the  usernames,
	      X.509  Subject  fields and Common	Name variables and it complies
	      to the RFC 2253, UTF-8 String  Representation  of	 Distinguished

	      The  no-remapping	 mode flag can be used with the	--compat-names
	      option to	be compatible with the now deprecated --no-name-remap-
	      ping option.  It is only available at the	server.	When this mode
	      flag is used, the	Common Name, Subject, and username strings are
	      allowed  to include any printable	character including space, but
	      excluding	control	characters such	as tab,	newline, and carriage-
	      return. no-remapping is only available on	the server side.

	      Please  note: This option	is immediately deprecated.  It is only
	      implemented to make the transition to the	 new  formatting  less
	      intrusive.   It  will be removed either in OpenVPN v2.4 or v2.5.
	      So please	 make  sure  you  use  the  --verify-x509-name	option
	      instead  of  --tls-remote	 as  soon  as possible and update your
	      scripts where necessary.

       --no-name-remapping (DEPRECATED)
	      The  --no-name-remapping	option	is   an	  alias	  for	--com-
	      pat-names	no-remapping.	It  ensures  compatibility with	server
	      configurations using the --no-name-remapping option.

	      Please note: This	option is now deprecated.  It will be  removed
	      either in	OpenVPN	v2.4 or	v2.5.  So please make sure you support
	      the new X.509 name formatting described with the	--compat-names
	      option as	soon as	possible.

       --port-share host port [dir]
	      When run in TCP server mode, share the OpenVPN port with another
	      application, such	as an HTTPS server.  If	OpenVPN	senses a  con-
	      nection  to  its	port which is using a non-OpenVPN protocol, it
	      will proxy the connection	to the server at host:port.  Currently
	      only  designed to	work with HTTP/HTTPS, though it	would be theo-
	      retically	possible to extend to other protocols such as ssh.

	      dir specifies an optional	directory where	a temporary file  with
	      name  N  containing  content C will be dynamically generated for
	      each proxy connection, where N is	 the  source  IP:port  of  the
	      client  connection and C is the source IP:port of	the connection
	      to the proxy receiver.  This directory can be used as a  dictio-
	      nary  by	the proxy receiver to determine	the origin of the con-
	      nection.	Each generated file will be automatically deleted when
	      the proxied connection is	torn down.

	      Not implemented on Windows.

   Client Mode
       Use  client  mode  when	connecting  to	an  OpenVPN  server  which has
       --server, --server-bridge, or --mode server in it's configuration.

	      A	helper directive designed to  simplify	the  configuration  of
	      OpenVPN's	client mode.  This directive is	equivalent to:


       --pull This  option  must  be used on a client which is connecting to a
	      multi-client server.  It indicates to  OpenVPN  that  it	should
	      accept  options  pushed by the server, provided they are part of
	      the legal	set of pushable	options	(note that the	--pull	option
	      is implied by --client ).

	      In  particular,  --pull  allows the server to push routes	to the
	      client, so you should not	use --pull or --client	in  situations
	      where  you  don't	 trust	the  server  to	 have control over the
	      client's routing table.

       --auth-user-pass	[up]
	      Authenticate with	server using username/password.	 up is a  file
	      containing username/password on 2	lines. If the password line is
	      missing, OpenVPN will prompt for one.

	      If up is omitted,	username/password will be  prompted  from  the

	      The server configuration must specify an --auth-user-pass-verify
	      script to	verify the username/password provided by the client.

       --auth-retry type
	      Controls how OpenVPN responds to username/password  verification
	      errors  such  as the client-side response	to an AUTH_FAILED mes-
	      sage from	the server or verification failure of the private  key

	      Normally	used  to  prevent  auth	errors from being fatal	on the
	      client side, and to permit username/password requeries  in  case
	      of error.

	      An  AUTH_FAILED message is generated by the server if the	client
	      fails --auth-user-pass authentication,  or  if  the  server-side
	      --client-connect	script returns an error	status when the	client
	      tries to connect.

	      type can be one of:

	      none -- Client will  exit	 with  a  fatal	 error	(this  is  the
	      nointeract  -- Client will retry the connection without requery-
	      ing for an --auth-user-pass username/password.  Use this	option
	      for unattended clients.
	      interact	--  Client  will requery for an	--auth-user-pass user-
	      name/password and/or private key password	 before	 attempting  a

	      Note  that  while	 this  option cannot be	pushed,	it can be con-
	      trolled from the management interface.

       --static-challenge t e
	      Enable static challenge/response protocol	using  challenge  text
	      t, with echo flag	given by e (0|1).

	      The  echo	 flag  indicates whether or not	the user's response to
	      the challenge should be echoed.

	      See management-notes.txt	in  the	 OpenVPN  distribution	for  a
	      description of the OpenVPN challenge/response protocol.

       --server-poll-timeout n
	      when  polling  possible remote servers to	connect	to in a	round-
	      robin fashion, spend no  more  than  n  seconds  waiting	for  a
	      response	before	trying	the  next  server.  As this only makes
	      sense in client-to-server	setups,	it cannot be used in point-to-
	      point setups using --secret symmetrical key mode.

       --explicit-exit-notify [n]
	      In  UDP  client mode or point-to-point mode, send	server/peer an
	      exit notification	if tunnel is restarted or OpenVPN  process  is
	      exited.	In client mode,	on exit/restart, this option will tell
	      the server to  immediately  close	 its  client  instance	object
	      rather  than waiting for a timeout.  The n parameter (default=1)
	      controls the maximum number of attempts that the client will try
	      to  resend the exit notification message.	 OpenVPN will not send
	      any exit notifications unless this option	is enabled.

   Data	Channel	Encryption Options:
       These options are meaningful for	both Static & TLS-negotiated key modes
       (must be	compatible between peers).

       --secret	file [direction]
	      Enable  Static  Key  encryption  mode (non-TLS).	Use pre-shared
	      secret file which	was generated with --genkey.

	      The optional direction parameter enables the use of  4  distinct
	      keys  (HMAC-send,	cipher-encrypt,	HMAC-receive, cipher-decrypt),
	      so that each data	flow direction has a different set of HMAC and
	      cipher keys.  This has a number of desirable security properties
	      including	eliminating certain kinds of DoS  and  message	replay

	      When  the	 direction parameter is	omitted, 2 keys	are used bidi-
	      rectionally, one for HMAC	and the	other  for  encryption/decryp-

	      The direction parameter should always be complementary on	either
	      side of the connection, i.e. one side should  use	 "0"  and  the
	      other should use "1", or both sides should omit it altogether.

	      The  direction  parameter	requires that file contains a 2048 bit
	      key.  While pre-1.5 versions of OpenVPN generate	1024  bit  key
	      files,  any  version  of	OpenVPN	 which	supports the direction
	      parameter, will also support 2048	bit key	file generation	 using
	      the --genkey option.

	      Static  key  encryption mode has certain advantages, the primary
	      being ease of configuration.

	      There are	no certificates	or certificate authorities or  compli-
	      cated  negotiation  handshakes and protocols.  The only require-
	      ment is that you have a pre-existing secure  channel  with  your
	      peer  (such  as  ssh ) to	initially copy the key.	 This require-
	      ment, along with the fact	that your key never changes unless you
	      manually	generate a new one, makes it somewhat less secure than
	      TLS mode (see below).  If	an attacker manages to steal your key,
	      everything that was ever encrypted with it is compromised.  Con-
	      trast that to the	perfect	forward	secrecy	features of  TLS  mode
	      (using  Diffie  Hellman key exchange), where even	if an attacker
	      was able to steal	your private key, he would gain	no information
	      to help him decrypt past sessions.

	      Another  advantageous  aspect  of	 Static	Key encryption mode is
	      that it is a handshake-free protocol without any	distinguishing
	      signature	 or  feature  (such  as	a header or protocol handshake
	      sequence)	that would mark	the ciphertext packets as being	gener-
	      ated  by	OpenVPN.   Anyone  eavesdropping on the	wire would see
	      nothing but random-looking data.

	      Alternative way of specifying the	optional  direction  parameter
	      for  the	--tls-auth  and	 --secret  options.  Useful when using
	      inline files (See	section	on inline files).

       --auth alg
	      Authenticate packets with	HMAC using  message  digest  algorithm
	      alg.   (The  default is SHA1 ).  HMAC is a commonly used message
	      authentication algorithm (MAC) that uses a data string, a	secure
	      hash algorithm, and a key, to produce a digital signature.

	      OpenVPN's	 usage of HMAC is to first encrypt a packet, then HMAC
	      the resulting ciphertext.

	      In static-key encryption mode, the HMAC key is included  in  the
	      key  file	 generated  by --genkey.  In TLS mode, the HMAC	key is
	      dynamically generated and	shared between peers via the TLS  con-
	      trol  channel.   If OpenVPN receives a packet with a bad HMAC it
	      will drop	the packet.  HMAC usually adds	16  or	20  bytes  per
	      packet.  Set alg=none to disable authentication.

	      For	 more	     information       on	HMAC	   see

       --cipher	alg
	      Encrypt data channel packets with	 cipher	 algorithm  alg.   The
	      default  is BF-CBC, an abbreviation for Blowfish in Cipher Block
	      Chaining mode.  Blowfish has the advantages of being fast,  very
	      secure,  and  allowing key sizes of up to	448 bits.  Blowfish is
	      designed to be used in situations	where keys are changed	infre-

	      For   more  information  on  blowfish,  see  http://www.counter-

	      To see other ciphers that	are available with  OpenVPN,  use  the
	      --show-ciphers option.

	      OpenVPN supports the CBC,	CFB, and OFB cipher modes, however CBC
	      is recommended and CFB and OFB  should  be  considered  advanced

	      Set alg=none to disable encryption.

       --keysize n
	      Size of cipher key in bits (optional).  If unspecified, defaults
	      to cipher-specific  default.   The  --show-ciphers  option  (see
	      below)  shows  all  available OpenSSL ciphers, their default key
	      sizes, and whether the key size can be  changed.	 Use  care  in
	      changing	a  cipher's  default  key size.	 Many ciphers have not
	      been extensively cryptanalyzed with  non-standard	 key  lengths,
	      and  a  larger  key may offer no real guarantee of greater secu-
	      rity, or may even	reduce security.

       --prng alg [nsl]
	      (Advanced) For PRNG (Pseudo-random number	generator), use	digest
	      algorithm	 alg  (default=sha1),  and set nsl (default=16)	to the
	      size in bytes of the nonce secret	length (between	16 and 64).

	      Set alg=none to disable the PRNG and use the OpenSSL  RAND_bytes
	      function	instead	 for  all  of  OpenVPN's  pseudo-random	number

       --engine	[engine-name]
	      Enable OpenSSL hardware-based crypto engine functionality.

	      If engine-name is	specified, use a specific crypto engine.   Use
	      the  --show-engines standalone option to list the	crypto engines
	      which are	supported by OpenSSL.

	      (Advanced) Disable OpenVPN's protection against replay  attacks.
	      Don't use	this option unless you are prepared to make a tradeoff
	      of greater efficiency in exchange	for less security.

	      OpenVPN provides datagram	replay protection by default.

	      Replay protection	is accomplished	by tagging each	outgoing data-
	      gram  with an identifier that is guaranteed to be	unique for the
	      key being	used.  The peer	that receives the datagram will	 check
	      for  the	uniqueness  of	the identifier.	 If the	identifier was
	      already received in a previous datagram, OpenVPN will  drop  the
	      packet.	Replay	protection is important	to defeat attacks such
	      as a SYN flood attack, where the attacker	listens	in  the	 wire,
	      intercepts  a  TCP  SYN packet (identifying it by	the context in
	      which it occurs in relation to other packets), then  floods  the
	      receiving	peer with copies of this packet.

	      OpenVPN's	replay protection is implemented in slightly different
	      ways, depending on the key management mode you have selected.

	      In Static	Key mode or when using an  CFB	or  OFB	 mode  cipher,
	      OpenVPN  uses  a	64  bit	unique identifier that combines	a time
	      stamp with an incrementing sequence number.

	      When using TLS mode for key exchange  and	 a  CBC	 cipher	 mode,
	      OpenVPN uses only	a 32 bit sequence number without a time	stamp,
	      since OpenVPN can	guarantee the uniqueness  of  this  value  for
	      each key.	 As in IPSec, if the sequence number is	close to wrap-
	      ping back	to zero, OpenVPN will trigger a	new key	exchange.

	      To check for replays, OpenVPN uses the sliding window  algorithm
	      used by IPSec.

       --replay-window n [t]
	      Use a replay protection sliding-window of	size n and a time win-
	      dow of t seconds.

	      By default n is 64 (the IPSec default) and t is 15 seconds.

	      This option is only relevant in  UDP  mode,  i.e.	  when	either
	      --proto udp is specifed, or no --proto option is specified.

	      When OpenVPN tunnels IP packets over UDP,	there is the possibil-
	      ity that packets might be	dropped	or  delivered  out  of	order.
	      Because  OpenVPN,	 like IPSec, is	emulating the physical network
	      layer, it	will accept an out-of-order packet sequence, and  will
	      deliver such packets in the same order they were received	to the
	      TCP/IP  protocol	stack,	provided  they	satisfy	 several  con-

	      (a)  The packet cannot be	a replay (unless --no-replay is	speci-
	      fied, which disables replay protection altogether).

	      (b) If a packet arrives out of order, it will only  be  accepted
	      if  the  difference  between its sequence	number and the highest
	      sequence number received so far is less than n.

	      (c) If a packet arrives out of order, it will only  be  accepted
	      if  it arrives no	later than t seconds after any packet contain-
	      ing a higher sequence number.

	      If you are using a network link with a large  pipeline  (meaning
	      that the product of bandwidth and	latency	is high), you may want
	      to use a larger value for	 n.   Satellite	 links	in  particular
	      often require this.

	      If  you  run  OpenVPN  at	 --verb	 4,  you  will see the message
	      "Replay-window backtrack occurred	[x]" every  time  the  maximum
	      sequence	number backtrack seen thus far increases.  This	can be
	      used to calibrate	n.

	      There is some controversy	on the appropriate method of  handling
	      packet reordering	at the security	layer.

	      Namely,  to  what	 extent	 should	the security layer protect the
	      encapsulated protocol from attacks which masquerade as the kinds
	      of  normal  packet  loss	and reordering that occur over IP net-

	      The IPSec	and OpenVPN approach is	 to  allow  packet  reordering
	      within a certain fixed sequence number window.

	      OpenVPN  adds  to	the IPSec model	by limiting the	window size in
	      time as well as sequence space.

	      OpenVPN also adds	TCP transport as an  option  (not  offered  by
	      IPSec)  in  which	 case OpenVPN can adopt	a very strict attitude
	      towards message deletion and reordering:	Don't allow it.	 Since
	      TCP  guarantees reliability, any packet loss or reordering event
	      can be assumed to	be an attack.

	      In this sense, it	could be argued	that TCP tunnel	 transport  is
	      preferred	 when  tunneling  non-IP  or UDP application protocols
	      which might be vulnerable	to a message  deletion	or  reordering
	      attack  which  falls within the normal operational parameters of
	      IP networks.

	      So I would make the statement that one  should  never  tunnel  a
	      non-IP  protocol	or  UDP	 application protocol over UDP,	if the
	      protocol might be	vulnerable to a	message	deletion or reordering
	      attack that falls	within the normal operating parameters of what
	      is to be expected	from the physical IP layer.   The  problem  is
	      easily fixed by simply using TCP as the VPN transport layer.

	      Silence  the output of replay warnings, which are	a common false
	      alarm on WiFi networks.  This option preserves the  security  of
	      the replay protection code without the verbosity associated with
	      warnings about duplicate packets.

       --replay-persist	file
	      Persist replay-protection	state across sessions  using  file  to
	      save and reload the state.

	      This  option  will strengthen protection against replay attacks,
	      especially when you are using OpenVPN in a dynamic context (such
	      as  with	--inetd)  when OpenVPN sessions	are frequently started
	      and stopped.

	      This option will keep a disk copy	of the current replay  protec-
	      tion  state  (i.e. the most recent packet	timestamp and sequence
	      number received from the remote peer), so	 that  if  an  OpenVPN
	      session  is stopped and restarted, it will reject	any replays of
	      packets which were already received by the prior session.

	      This option only makes sense when	replay protection  is  enabled
	      (the  default)  and you are using	either --secret	(shared-secret
	      key mode)	or TLS mode with --tls-auth.

	      (Advanced) Disable OpenVPN's use of  IV  (cipher	initialization
	      vector).	 Don't use this	option unless you are prepared to make
	      a	tradeoff of greater efficiency in exchange for less  security.

	      OpenVPN  uses  an	IV by default, and requires it for CFB and OFB
	      cipher modes (which are totally insecure without it).  Using  an
	      IV  is  important	 for security when multiple messages are being
	      encrypted/decrypted with the same	key.

	      IV is implemented	differently depending on the cipher mode used.

	      In CBC mode, OpenVPN uses	a pseudo-random	IV for each packet.

	      In  CFB/OFB mode,	OpenVPN	uses a unique sequence number and time
	      stamp as the IV.	In fact, in CFB/OFB mode, OpenVPN uses a data-
	      gram  space-saving  optimization that uses the unique identifier
	      for datagram replay protection as	the IV.

	      Enable prediction	resistance on PolarSSL's RNG.

	      Enabling prediction resistance causes the	RNG to reseed in  each
	      call  for	 random.  Reseeding this often can quickly deplete the
	      kernel entropy pool.

	      If you need this option, please consider running a  daemon  that
	      adds entropy to the kernel pool.

	      Note  that this option only works	with PolarSSL versions greater
	      than 1.1.

	      Do a self-test of	OpenVPN's crypto  options  by  encrypting  and
	      decrypting  test	packets	 using	the  data  channel  encryption
	      options specified	above.	This option does not require a peer to
	      function,	 and  therefore	 can  be  specified  without  --dev or

	      The typical usage	of --test-crypto would be something like this:

	      openvpn --test-crypto --secret key


	      openvpn --test-crypto --secret key --verb	9

	      This  option  is	very  useful to	test OpenVPN after it has been
	      ported to	a new platform,	or to isolate  problems	 in  the  com-
	      piler,  OpenSSL crypto library, or OpenVPN's crypto code.	 Since
	      it is a self-test	mode, problems with encryption and authentica-
	      tion can be debugged independently of network and	tunnel issues.

   TLS Mode Options:
       TLS mode	is the most powerful crypto mode of OpenVPN in	both  security
       and flexibility.	 TLS mode works	by establishing	control	and data chan-
       nels which are multiplexed over a single	TCP/UDP	port.  OpenVPN	initi-
       ates  a	TLS  session  over the control channel and uses	it to exchange
       cipher and HMAC keys to protect the data	 channel.   TLS	 mode  uses  a
       robust  reliability layer over the UDP connection for all control chan-
       nel communication, while	the data channel, over which encrypted	tunnel
       data  passes,  is  forwarded  without any mediation.  The result	is the
       best of both worlds: a fast data	channel	that forwards  over  UDP  with
       only  the  overhead of encrypt, decrypt,	and HMAC functions, and	a con-
       trol channel that provides all of the security features of TLS, includ-
       ing   certificate-based	 authentication	 and  Diffie  Hellman  forward

       To use TLS mode,	each peer that runs OpenVPN should have	its own	 local
       certificate/key	pair ( --cert and --key	), signed by the root certifi-
       cate which is specified in --ca.

       When two	OpenVPN	peers connect, each presents its local certificate  to
       the other.  Each	peer will then check that its partner peer presented a
       certificate which was signed by the master root certificate  as	speci-
       fied in --ca.

       If  that	 check	on  both peers succeeds, then the TLS negotiation will
       succeed,	both OpenVPN peers will	exchange temporary session  keys,  and
       the tunnel will begin passing data.

       The  OpenVPN  distribution  contains  a set of scripts for managing RSA
       certificates & keys, located in the easy-rsa subdirectory.

       The easy-rsa package is also rendered in	web  form  here:  http://open-

	      Enable  TLS  and	assume server role during TLS handshake.  Note
	      that OpenVPN is designed as  a  peer-to-peer  application.   The
	      designation of client or server is only for the purpose of nego-
	      tiating the TLS control channel.

	      Enable TLS and assume client role	during TLS handshake.

       --ca file
	      Certificate authority (CA) file in .pem format, also referred to
	      as  the  root certificate.  This file can	have multiple certifi-
	      cates in .pem format, concatenated together.  You	can  construct
	      your  own	 certificate  authority	certificate and	private	key by
	      using a command such as:

	      openssl req -nodes -new -x509 -keyout ca.key -out	ca.crt

	      Then edit	your openssl.cnf file and edit the  certificate	 vari-
	      able to point to your new	root certificate ca.crt.

	      For  testing  purposes only, the OpenVPN distribution includes a
	      sample CA	certificate (ca.crt).  Of course you should never  use
	      the  test	certificates and test keys distributed with OpenVPN in
	      a	production environment,	since by virtue	of the fact that  they
	      are distributed with OpenVPN, they are totally insecure.

       --capath	dir
	      Directory	  containing  trusted  certificates  (CAs  and	CRLs).
	      Available	with OpenSSL version >=	0.9.7 dev.  Not	available with

	      When using the --capath option, you are required to supply valid
	      CRLs for the CAs too.  CAs in the	capath directory are  expected
	      to   be  named  <hash>.<n>.   CRLs  are  expected	 to  be	 named
	      <hash>.r<n>.  See	the -CApath option of openssl verify , and the
	      -hash  option  of	openssl	x509 and openssl crl for more informa-

       --dh file
	      File  containing	Diffie	Hellman	 parameters  in	 .pem	format
	      (required	for --tls-server only).	Use

	      openssl dhparam -out dh1024.pem 1024

	      to  generate  your  own,	or  use	 the  existing dh1024.pem file
	      included with the	OpenVPN	distribution.  Diffie Hellman  parame-
	      ters may be considered public.

       --cert file
	      Local peer's signed certificate in .pem format --	must be	signed
	      by a certificate authority whose certificate is  in  --ca	 file.
	      Each peer	in an OpenVPN link running in TLS mode should have its
	      own certificate and private key file.  In	 addition,  each  cer-
	      tificate	should	have  been  signed by the key of a certificate
	      authority	whose public  key  resides  in	the  --ca  certificate
	      authority	 file.	 You  can  easily  make	 your  own certificate
	      authority	(see above) or pay money to use	a  commercial  service
	      such as (in which case	you will be helping to finance
	      the world's second space tourist :).  To generate	a certificate,
	      you can use a command such as:

	      openssl req -nodes -new -keyout mycert.key -out mycert.csr

	      If  your	certificate  authority	private	 key  lives on another
	      machine, copy the	certificate signing  request  (mycert.csr)  to
	      this  other  machine  (this can be done over an insecure channel
	      such as email).  Now sign	the certificate	with  a	 command  such

	      openssl ca -out mycert.crt -in mycert.csr

	      Now  copy	 the  certificate  (mycert.crt)	back to	the peer which
	      initially	generated the .csr file	(this can  be  over  a	public
	      medium).	Note that the openssl ca command reads the location of
	      the certificate authority	key from its configuration  file  such
	      as  /usr/share/ssl/openssl.cnf --	note also that for certificate
	      authority	functions, you must set	up the files index.txt (may be
	      empty) and serial	(initialize to 01 ).

       --extra-certs file
	      Specify  a  file	containing one or more PEM certs (concatenated
	      together)	that complete the local	certificate chain.

	      This option is useful for	"split"	CAs, where the CA  for	server
	      certs  is	different than the CA for client certs.	 Putting certs
	      in this file allows them to be used to complete the  local  cer-
	      tificate	chain without trusting them to verify the peer-submit-
	      ted certificate, as would	be the case if the certs  were	placed
	      in the ca	file.

       --key file
	      Local  peer's  private  key in .pem format.  Use the private key
	      which was	generated when you built your peer's certificate  (see
	      --cert file above).

       --tls-version-min version ['or-highest']
	      Enable  TLS version negotiation, and set the minimum TLS version
	      we will accept from the peer (default is "1.0").	 Examples  for
	      version  include	"1.0",	"1.1",	or  "1.2".  If 'or-highest' is
	      specified	and version is not recognized, we will only accept the
	      highest TLS version supported by the local SSL implementation.

	      Also see --tls-version-max below,	for information	on compatibil-

       --tls-version-max version
	      Set the maximum TLS version we will use (default is the  highest
	      version  supported).  Examples for version include "1.0",	"1.1",
	      or "1.2".

	      If and only if this is set to 1.0,  and  OpenSSL	is  used  (not
	      PolarSSL), then OpenVPN will set up OpenSSL to use a fixed TLSv1
	      handshake. All other configurations will	autonegotiate  in  the
	      given  limits,  and  the choice of handshake versions is left to
	      the SSL implementation.

       --pkcs12	file
	      Specify a	PKCS #12 file containing local private key, local cer-
	      tificate,	 and  root  CA	certificate.   This option can be used
	      instead  of  --ca,  --cert,  and	--key.	 Not  available	  with

       --verify-hash hash
	      Specify  SHA1 fingerprint	for level-1 cert.  The level-1 cert is
	      the CA (or intermediate cert) that signs the  leaf  certificate,
	      and is one removed from the leaf certificate in the direction of
	      the root.	 When accepting	a connection from a peer, the  level-1
	      cert  fingerprint	 must  match  hash or certificate verification
	      will  fail.   Hash  is  specified	 as  XX:XX:...	 For  example:

       --pkcs11-cert-private [0|1]...
	      Set  if  access  to certificate object should be performed after
	      login.  Every provider has its own setting.

       --pkcs11-id name
	      Specify the serialized certificate id to be used.	The id can  be
	      gotten by	the standalone --show-pkcs11-ids option.

	      Acquire  PKCS#11	id  from  management interface.	In this	case a
	      NEED-STR 'pkcs11-id-request' real-time  message  will  be	 trig-
	      gered,  application  may use pkcs11-id-count command to retrieve
	      available	number of certificates,	and pkcs11-id-get  command  to
	      retrieve certificate id and certificate body.

       --pkcs11-pin-cache seconds
	      Specify  how  many seconds the PIN can be	cached,	the default is
	      until the	token is removed.

       --pkcs11-protected-authentication [0|1]...
	      Use PKCS#11 protected authentication path, useful	for  biometric
	      and  external  keypad  devices.  Every provider has its own set-

       --pkcs11-providers provider...
	      Specify a	RSA Security Inc. PKCS #11 Cryptographic Token	Inter-
	      face  (Cryptoki)	providers  to  load.   This option can be used
	      instead of --cert, --key,	and --pkcs12.

	      If p11-kit is present on the system, its	module
	      will   be	 loaded	 by  default  if  either  the  --pkcs11-id  or
	      --pkcs11-id-management	options	   are	  specified    without
	      --pkcs11-provider	being given.

       --pkcs11-private-mode mode...
	      Specify  which  method  to  use  in order	to perform private key
	      operations.   A  different  mode	can  be	 specified  for	  each
	      provider.	  Mode is encoded as hex number, and can be a mask one
	      of the following:

	      0	(default) -- Try to determine automatically.
	      1	-- Use sign.
	      2	-- Use sign recover.
	      4	-- Use decrypt.
	      8	-- Use unwrap.

       --cryptoapicert select-string
	      Load the certificate and private key from	the  Windows  Certifi-
	      cate System Store	(Windows/OpenSSL Only).

	      Use this option instead of --cert	and --key.

	      This  makes it possible to use any smart card, supported by Win-
	      dows, but	also any kind of certificate,  residing	 in  the  Cert
	      Store,  where  you  have access to the private key.  This	option
	      has been tested with a couple of different smart cards (GemSAFE,
	      Cryptoflex, and Swedish Post Office eID) on the client side, and
	      also an imported PKCS12 software certificate on the server side.

	      To select	a certificate, based on	a substring search in the cer-
	      tificate's subject:

	      cryptoapicert "SUBJ:Peter	Runestig"

	      To select	a certificate, based on	certificate's thumbprint:

	      cryptoapicert "THUMB:f6 49 24 41 01 b4 ..."

	      The thumbprint hex string	can easily be copy-and-pasted from the
	      Windows Certificate Store	GUI.

       --key-method m
	      Use  data	channel	key negotiation	method m.  The key method must
	      match on both sides of the connection.

	      After OpenVPN negotiates a TLS session, a	new set	 of  keys  for
	      protecting  the  tunnel  data channel is generated and exchanged
	      over the TLS session.

	      In method	1 (the default for OpenVPN 1.x), both  sides  generate
	      random  encrypt  and  HMAC-send  keys which are forwarded	to the
	      other host over the TLS channel.

	      In method	2, (the	default	for OpenVPN 2.0) the client  generates
	      a	 random	key.  Both client and server also generate some	random
	      seed material.  All key source material is  exchanged  over  the
	      TLS  channel.  The  actual  keys are generated using the TLS PRF
	      function,	taking source entropy from  both  client  and  server.
	      Method  2	 is  designed  to  closely parallel the	key generation
	      process used by TLS 1.0.

	      Note that	in TLS mode, two separate levels of keying occur:

	      (1) The TLS connection is	initially negotiated, with both	 sides
	      of  the connection producing certificates	and verifying the cer-
	      tificate (or other authentication	info provided)	of  the	 other
	      side.  The --key-method parameter	has no effect on this process.

	      (2) After	the TLS	connection is established, the tunnel  session
	      keys  are	 separately  negotiated	 over  the existing secure TLS
	      channel.	Here, --key-method determines the  derivation  of  the
	      tunnel session keys.

       --tls-cipher l
	      A	list l of allowable TLS	ciphers	delimited by a colon (":").

	      This  setting  can  be used to ensure that certain cipher	suites
	      are used (or not used) for the TLS connection.  OpenVPN uses TLS
	      to secure	the control channel, over which	the keys that are used
	      to protect the actual VPN	traffic	are exchanged.

	      The supplied list	of ciphers is  (after  potential  OpenSSL/IANA
	      name translation)	simply supplied	to the crypto library.	Please
	      see the OpenSSL and/or PolarSSL documentation for	details	on the
	      cipher list interpretation.

	      Use  --show-tls  to  see a list of TLS ciphers supported by your
	      crypto library.

	      Warning!	--tls-cipher is	an expert feature,  which  -  if  used
	      correcly - can improve the security of your VPN connection.  But
	      it is also easy to unwittingly use it to carefully align	a  gun
	      with your	foot, or just break your connection.  Use with care!

	      The default for --tls-cipher is to use PolarSSL's	default	cipher
	      list	    when	  using		 PolarSSL	    or
	      "DEFAULT:!EXP:!LOW:!MEDIUM:!PSK:!SRP:!kRSA"  when	using OpenSSL.

       --tls-timeout n
	      Packet retransmit	timeout	on TLS control channel if no  acknowl-
	      edgment  from remote within n seconds (default=2).  When OpenVPN
	      sends a control packet to	its peer, it will expect to receive an
	      acknowledgement  within  n  seconds  or  it  will	retransmit the
	      packet, subject to a  TCP-like  exponential  backoff  algorithm.
	      This  parameter  only  applies to	control	channel	packets.  Data
	      channel packets (which carry encrypted tunnel  data)  are	 never
	      acknowledged, sequenced, or retransmitted	by OpenVPN because the
	      higher level network protocols running on	top of the tunnel such
	      as TCP expect this role to be left to them.

       --reneg-bytes n
	      Renegotiate  data	 channel  key  after  n	bytes sent or received
	      (disabled	by default).  OpenVPN allows the lifetime of a key  to
	      be  expressed as a number	of bytes encrypted/decrypted, a	number
	      of packets, or a number of seconds.  A key renegotiation will be
	      forced if	any of these three criteria are	met by either peer.

       --reneg-pkts n
	      Renegotiate  data	 channel key after n packets sent and received
	      (disabled	by default).

       --reneg-sec n
	      Renegotiate data channel key after n seconds (default=3600).

	      When using dual-factor authentication, note  that	 this  default
	      value  may  cause	 the  end user to be challenged	to reauthorize
	      once per hour.

	      Also, keep in mind that this option can  be  used	 on  both  the
	      client  and  server,  and	whichever uses the lower value will be
	      the one to trigger the renegotiation.  A common  mistake	is  to
	      set  --reneg-sec	to  a  higher  value  on  either the client or
	      server, while the	other side of the connection  is  still	 using
	      the  default  value of 3600 seconds, meaning that	the renegotia-
	      tion will	still occur once per 3600 seconds.  The	solution is to
	      increase --reneg-sec on both the client and server, or set it to
	      0	on one side of the connection (to disable), and	to your	chosen
	      value on the other side.

       --hand-window n
	      Handshake	 Window	 --  the  TLS-based key	exchange must finalize
	      within n seconds of handshake initiation by any peer (default  =
	      60  seconds).   If  the handshake	fails we will attempt to reset
	      our connection with our peer and try again.  Even	in  the	 event
	      of  handshake  failure we	will still use our expiring key	for up
	      to --tran-window seconds to maintain continuity of  transmission
	      of tunnel	data.

       --tran-window n
	      Transition  window  --  our  old	key can	live this many seconds
	      after a new a key	renegotiation begins (default =	3600 seconds).
	      This  feature  allows  for a graceful transition from old	to new
	      key, and removes the key renegotiation sequence from the	criti-
	      cal path of tunnel data forwarding.

	      After  initially	connecting  to a remote	peer, disallow any new
	      connections.  Using this option means that a remote peer	cannot
	      connect, disconnect, and then reconnect.

	      If  the  daemon  is reset	by a signal or --ping-restart, it will
	      allow one	new connection.

	      --single-session can be used with	--ping-exit or	--inactive  to
	      create a single dynamic session that will	exit when finished.

	      Exit on TLS negotiation failure.

       --tls-auth file [direction]
	      Add an additional	layer of HMAC authentication on	top of the TLS
	      control channel to protect against DoS attacks.

	      In a nutshell, --tls-auth	enables	a kind of "HMAC	 firewall"  on
	      OpenVPN's	 TCP/UDP port, where TLS control channel packets bear-
	      ing an incorrect HMAC signature can be dropped immediately with-
	      out response.

	      file  (required)	is  a key file which can be in one of two for-

	      (1) An OpenVPN static key	file generated by  --genkey  (required
	      if direction parameter is	used).

	      (2)  DEPRECATED  A  freeform  passphrase file.  In this case the
	      HMAC key will be derived by taking a secure hash of  this	 file,
	      similar  to the md5sum(1)	or sha1sum(1) commands.	This option is
	      deprecated and will  stop	 working  in  OpenVPN  2.4  and	 newer

	      OpenVPN  will  first  try	 format	 (1), and if the file fails to
	      parse as a static	key file, format (2) will be used.

	      See the --secret option for more	information  on	 the  optional
	      direction	parameter.

	      --tls-auth is recommended	when you are running OpenVPN in	a mode
	      where it is listening for	packets	from any IP address,  such  as
	      when  --remote  is  not specified, or --remote is	specified with

	      The rationale for	this feature is	as follows.   TLS  requires  a
	      multi-packet  exchange before it is able to authenticate a peer.
	      During this time before authentication,  OpenVPN	is  allocating
	      resources	 (memory  and CPU) to this potential peer.  The	poten-
	      tial peer	is also	exposing many parts of OpenVPN and the OpenSSL
	      library  to  the packets it is sending.  Most successful network
	      attacks today seek to either exploit bugs	in programs  (such  as
	      buffer  overflow	attacks) or force a program to consume so many
	      resources	that it	becomes	unusable.  Of course the first line of
	      defense  is always to produce clean, well-audited	code.  OpenVPN
	      has been written with buffer overflow attack prevention as a top
	      priority.	  But  as  history  has	shown, many of the most	widely
	      used network applications	have, from time	 to  time,  fallen  to
	      buffer overflow attacks.

	      So  as  a	 second	 line  of defense, OpenVPN offers this special
	      layer of authentication on top of	the  TLS  control  channel  so
	      that  every packet on the	control	channel	is authenticated by an
	      HMAC signature and a unique ID for replay	protection.  This sig-
	      nature  will  also  help protect against DoS (Denial of Service)
	      attacks.	An important rule of thumb in  reducing	 vulnerability
	      to  DoS  attacks is to minimize the amount of resources a	poten-
	      tial, but	as yet unauthenticated,	client is able to consume.

	      --tls-auth does this by signing every TLS	control	channel	packet
	      with  an HMAC signature, including packets which are sent	before
	      the TLS level has	had a chance to	authenticate  the  peer.   The
	      result  is  that	packets	 without  the correct signature	can be
	      dropped immediately upon reception, before they have a chance to
	      consume  additional system resources such	as by initiating a TLS
	      handshake.   --tls-auth  can  be	strengthened  by  adding   the
	      --replay-persist option which will keep OpenVPN's	replay protec-
	      tion state in a file so that it is not lost across restarts.

	      It should	be emphasized that this	feature	is optional  and  that
	      the  passphrase/key file used with --tls-auth gives a peer noth-
	      ing more than the	power to initiate a TLS	handshake.  It is  not
	      used to encrypt or authenticate any tunnel data.

       --askpass [file]
	      Get  certificate	password from console or file before we	daemo-

	      For the extremely	security conscious, it is possible to  protect
	      your  private  key  with	a password.  Of	course this means that
	      every time the OpenVPN daemon is started you must	 be  there  to
	      type  the	 password.   The  --askpass option allows you to start
	      OpenVPN from the command line.  It will query you	for a password
	      before  it daemonizes.  To protect a private key with a password
	      you should omit the -nodes option	when you use the openssl  com-
	      mand line	tool to	manage certificates and	private	keys.

	      If  file	is specified, read the password	from the first line of
	      file.  Keep in mind that storing your password in	a  file	 to  a
	      certain  extent invalidates the extra security provided by using
	      an encrypted key.

	      Don't cache --askpass or --auth-user-pass	username/passwords  in
	      virtual memory.

	      If  specified,  this directive will cause	OpenVPN	to immediately
	      forget username/password inputs  after  they  are	 used.	 As  a
	      result,  when  OpenVPN needs a username/password,	it will	prompt
	      for input	from stdin, which may be  multiple  times  during  the
	      duration of an OpenVPN session.

	      When  using  --auth-nocache  in combination with a user/password
	      file and --chroot	or --daemon, make  sure	 to  use  an  absolute

	      This  directive  does not	affect the --http-proxy	username/pass-
	      word.  It	is always cached.

       --tls-verify cmd
	      Run command cmd to verify	the X509 name of a pending TLS connec-
	      tion  that has otherwise passed all other	tests of certification
	      (except for revocation via --crl-verify directive;  the  revoca-
	      tion test	occurs after the --tls-verify test).

	      cmd  should return 0 to allow the	TLS handshake to proceed, or 1
	      to fail.

	      cmd consists of  a  path	to  script  (or	 executable  program),
	      optionally  followed by arguments. The path and arguments	may be
	      single- or double-quoted and/or escaped using a  backslash,  and
	      should be	separated by one or more spaces.

	      When  cmd	is executed two	arguments are appended after any argu-
	      ments specified in cmd , as follows:

	      cmd certificate_depth subject

	      These arguments are, respectively, the current certificate depth
	      and the X509 common name (cn) of the peer.

	      This  feature is useful if the peer you want to trust has	a cer-
	      tificate which was signed	by a certificate  authority  who  also
	      signed many other	certificates, where you	don't necessarily want
	      to trust all of them, but	rather be selective about  which  peer
	      certificate you will accept.  This feature allows	you to write a
	      script which will	test the X509 name on a	certificate and	decide
	      whether  or not it should	be accepted.  For a simple perl	script
	      which will test the common name field on	the  certificate,  see
	      the file verify-cn in the	OpenVPN	distribution.

	      See  the	"Environmental Variables" section below	for additional
	      parameters passed	as environmental variables.

       --tls-export-cert directory
	      Store the	certificates the clients uses upon connection to  this
	      directory. This will be done before --tls-verify is called.  The
	      certificates will	use a temporary	name and will be deleted  when
	      the  tls-verify script returns.  The file	name used for the cer-
	      tificate is available via	the peer_cert environment variable.

       --x509-username-field [ext:]fieldname
	      Field in the X.509 certificate subject to	be used	as  the	 user-
	      name  (default=CN).   Typically,	this  option is	specified with
	      fieldname	as either of the following:

	      --x509-username-field emailAddress
	      --x509-username-field ext:subjectAltName

	      The first	example	uses the value of the "emailAddress" attribute
	      in  the certificate's Subject field as the username.  The	second
	      example uses the ext: prefix to signify that the X.509 extension
	      fieldname	"subjectAltName" be searched for an rfc822Name (email)
	      field to be used as the username.	 In cases where	there are mul-
	      tiple  email  addresses in ext:fieldname,	the last occurrence is

	      When this	option is used,	 the  --verify-x509-name  option  will
	      match against the	chosen fieldname instead of the	Common Name.

	      Please  note:  This  option  has a feature which will convert an
	      all-lowercase fieldname to uppercase characters, e.g., ou	-> OU.
	      A	 mixed-case  fieldname	or  one	having the ext:	prefix will be
	      left as-is.  This	automatic upcasing feature is  deprecated  and
	      will be removed in a future release.

       --tls-remote name (DEPRECATED)
	      Accept  connections  only	 from  a host with X509	name or	common
	      name equal to name.  The remote host must	also  pass  all	 other
	      tests of verification.

	      NOTE:  Because tls-remote	may test against a common name prefix,
	      only use this option when	you are	using OpenVPN with a custom CA
	      certificate  that	 is under your control.	 Never use this	option
	      when your	client certificates are	signed by a third party,  such
	      as a commercial web CA.

	      Name can also be a common	name prefix, for example if you	want a
	      client to	only accept  connections  to  "Server-1",  "Server-2",
	      etc., you	can simply use --tls-remote Server

	      Using a common name prefix is a useful alternative to managing a
	      CRL (Certificate Revocation List)	on the client, since it	allows
	      the  client  to refuse all certificates except for those associ-
	      ated with	designated servers.

	      --tls-remote is a	useful replacement for the --tls-verify	option
	      to  verify  the  remote  host,  because  --tls-remote works in a
	      --chroot environment too.

	      Please also note:	This option is now  deprecated.	  It  will  be
	      removed either in	OpenVPN	v2.4 or	v2.5.  So please make sure you
	      support the new X.509 name formatting described with the	--com-
	      pat-names	option as soon as possible by updating your configura-
	      tions to use --verify-x509-name instead.

       --verify-x509-name name type
	      Accept connections only if a host's X.509	name is	equal to name.
	      The  remote host must also pass all other	tests of verification.

	      Which X.509 name is compared to name depends on the  setting  of
	      type.   type  can	 be "subject" to match the complete subject DN
	      (default), "name"	to match a subject  RDN	 or  "name-prefix"  to
	      match  a	subject	 RDN  prefix.	Which  RDN is verified as name
	      depends on the --x509-username-field option. But it defaults  to
	      the  common  name	 (CN),	e.g.  a	 certificate with a subject DN
	      "C=KG, ST=NA, L=Bishkek, CN=Server-1" would be matched by:

	      --verify-x509-name 'C=KG,	 ST=NA,	 L=Bishkek,  CN=Server-1'  and
	      --verify-x509-name   Server-1  name  or  you  could  use	--ver-
	      ify-x509-name Server- name-prefix	if you want a client  to  only
	      accept connections to "Server-1",	"Server-2", etc.

	      --verify-x509-name  is a useful replacement for the --tls-verify
	      option to	verify the  remote  host,  because  --verify-x509-name
	      works in a --chroot environment without any dependencies.

	      Using  a	name  prefix is	a useful alternative to	managing a CRL
	      (Certificate Revocation List) on the client, since it allows the
	      client  to  refuse  all certificates except for those associated
	      with designated servers.

	      NOTE: Test against a name	prefix only when you are using OpenVPN
	      with  a custom CA	certificate that is under your control.	 Never
	      use this option with type	"name-prefix" when  your  client  cer-
	      tificates	 are signed by a third party, such as a	commercial web

       --x509-track attribute
	      Save peer	X509 attribute value in	environment for	use by plugins
	      and  management  interface.   Prepend a '+' to attribute to save
	      values  from  full  cert	chain.	 Values	 will  be  encoded  as
	      X509_<depth>_<attribute>=<value>.	 Multiple --x509-track options
	      can be defined to	track multiple attributes.  Not	available with

       --ns-cert-type client|server
	      Require  that  peer  certificate	was  signed  with  an explicit
	      nsCertType designation of	"client" or "server".

	      This is a	useful security	option for clients, to ensure that the
	      host they	connect	with is	a designated server.

	      See  the	easy-rsa/build-key-server script for an	example	of how
	      to generate a certificate	 with  the  nsCertType	field  set  to

	      If the server certificate's nsCertType field is set to "server",
	      then the clients can verify this with --ns-cert-type server.

	      This is an important security precaution to  protect  against  a
	      man-in-the-middle	 attack	where an authorized client attempts to
	      connect to another client	 by  impersonating  the	 server.   The
	      attack  is  easily prevented by having clients verify the	server
	      certificate using	any one	of --ns-cert-type, --verify-x509-name,
	      or --tls-verify.

       --remote-cert-ku	v...
	      Require  that  peer  certificate was signed with an explicit key

	      This is a	useful security	option for clients, to ensure that the
	      host they	connect	to is a	designated server.

	      The  key usage should be encoded in hex, more than one key usage
	      can be specified.

       --remote-cert-eku oid
	      Require that  peer  certificate  was  signed  with  an  explicit
	      extended key usage.

	      This is a	useful security	option for clients, to ensure that the
	      host they	connect	to is a	designated server.

	      The extended key usage should be encoded	in  oid	 notation,  or
	      OpenSSL symbolic representation.

       --remote-cert-tls client|server
	      Require  that  peer  certificate was signed with an explicit key
	      usage and	extended key usage based on RFC3280 TLS	rules.

	      This is a	useful security	option for clients, to ensure that the
	      host they	connect	to is a	designated server.

	      The   --remote-cert-tls	client	 option	  is   equivalent   to
	      --remote-cert-ku 80 08  88  --remote-cert-eku  "TLS  Web	Client

	      The key usage is digitalSignature	and/or keyAgreement.

	      The   --remote-cert-tls	server	 option	  is   equivalent   to
	      --remote-cert-ku a0 88 --remote-cert-eku "TLS Web	Server Authen-

	      The key usage is digitalSignature	and ( keyEncipherment or keyA-
	      greement ).

	      This is an important security precaution to  protect  against  a
	      man-in-the-middle	 attack	where an authorized client attempts to
	      connect to another client	 by  impersonating  the	 server.   The
	      attack  is  easily prevented by having clients verify the	server
	      certificate  using  any	one   of   --remote-cert-tls,	--ver-
	      ify-x509-name, or	--tls-verify.

       --crl-verify crl	['dir']
	      Check peer certificate against the file crl in PEM format.

	      A	 CRL  (certificate  revocation list) is	used when a particular
	      key is compromised but when the overall PKI is still intact.

	      Suppose you had a	PKI consisting of a CA,	root certificate,  and
	      a	number of client certificates.	Suppose	a laptop computer con-
	      taining a	client key and certificate was stolen.	By adding  the
	      stolen certificate to the	CRL file, you could reject any connec-
	      tion which attempts to use  it,  while  preserving  the  overall
	      integrity	of the PKI.

	      The  only	 time when it would be necessary to rebuild the	entire
	      PKI from scratch would be	if the root certificate	key itself was

	      If  the  optional	dir flag is specified, enable a	different mode
	      where crl	is a  directory	 containing  files  named  as  revoked
	      serial  numbers  (the files may be empty,	the contents are never
	      read).  If a client requests a connection, where the client cer-
	      tificate	serial	number	(decimal string) is the	name of	a file
	      present in the directory,	it will	be rejected.

	      Note: As the crl file (or	directory) is read every time  a  peer
	      connects,	 if you	are dropping root privileges with --user, make
	      sure that	this user has sufficient privileges to read the	 file.

   SSL Library information:
	      (Standalone) Show	all cipher algorithms to use with the --cipher

	      (Standalone) Show	all message digest algorithms to use with  the
	      --auth option.

	      (Standalone)  Show  all  TLS  ciphers  supported	by  the	crypto
	      library.	OpenVPN	uses TLS to secure the control	channel,  over
	      which  the  keys that are	used to	protect	the actual VPN traffic
	      are exchanged.  The TLS ciphers  will  be	 sorted	 from  highest
	      preference (most secure) to lowest.

	      Be  aware	 that whether a	cipher suite in	this list can actually
	      work depends on the specific setup  of  both  peers  (e.g.  both
	      peers  must  support  the	cipher,	and an ECDSA cipher suite will
	      not work if you are using	an RSA certificate, etc.).

	      (Standalone)  Show  currently  available	hardware-based	crypto
	      acceleration engines supported by	the OpenSSL library.

   Generate a random key:
       Used only for non-TLS static key	encryption mode.

	      (Standalone)  Generate  a	 random	 key  to  be  used as a	shared
	      secret, for use with the --secret	option.	  This	file  must  be
	      shared  with the peer over a pre-existing	secure channel such as

       --secret	file
	      Write key	to file.

   TUN/TAP persistent tunnel config mode:
       Available with linux 2.4.7+.  These options comprise a standalone  mode
       of OpenVPN which	can be used to create and delete persistent tunnels.

	      (Standalone)  Create a persistent	tunnel on platforms which sup-
	      port them	such as	Linux.	Normally TUN/TAP  tunnels  exist  only
	      for  the period of time that an application has them open.  This
	      option takes advantage of	the TUN/TAP driver's ability to	 build
	      persistent  tunnels that live through multiple instantiations of
	      OpenVPN and die only when	they are deleted  or  the  machine  is

	      One  of the advantages of	persistent tunnels is that they	elimi-
	      nate the need for	separate --up and --down scripts  to  run  the
	      appropriate  ifconfig(8)	and route(8) commands.	These commands
	      can be placed in the the same shell script which starts or  ter-
	      minates an OpenVPN session.

	      Another  advantage is that open connections through the TUN/TAP-
	      based tunnel will	not be reset if	 the  OpenVPN  peer  restarts.
	      This can be useful to provide uninterrupted connectivity through
	      the tunnel in the	event of a DHCP	reset of the peer's public  IP
	      address (see the --ipchange option above).

	      One  disadvantage	 of persistent tunnels is that it is harder to
	      automatically configure their  MTU  value	 (see  --link-mtu  and
	      --tun-mtu	above).

	      On some platforms	such as	Windows, TAP-Win32 tunnels are persis-
	      tent by default.

	      (Standalone) Remove a persistent tunnel.

       --dev tunX | tapX
	      TUN/TAP device

       --user user
	      Optional user to be owner	of this	tunnel.

       --group group
	      Optional group to	be owner of this tunnel.

   Windows-Specific Options:
       --win-sys path
	      Set the Windows system directory pathname	to  use	 when  looking
	      for  system  executables	such  as  route.exe and	netsh.exe.  By
	      default, if this directive is not	specified,  OpenVPN  will  use
	      the SystemRoot environment variable.

	      This  option have	changed	behaviour in OpenVPN 2.3.  Earlier you
	      had to define --win-sys env to use  the  SystemRoot  environment
	      variable,	 otherwise  it	defaulted  to  C:\WINDOWS.   It	is not
	      needed to	use the	env keyword any	more,  and  it	will  just  be
	      ignored.	A warning is logged when this is found in the configu-
	      ration file.

       --ip-win32 method
	      When using --ifconfig on Windows,	set the	TAP-Win32  adapter  IP
	      address  and netmask using method.  Don't	use this option	unless
	      you are also using --ifconfig.

	      manual --	Don't set the IP  address  or  netmask	automatically.
	      Instead output a message to the console telling the user to con-
	      figure the adapter manually and indicating the IP/netmask	 which
	      OpenVPN expects the adapter to be	set to.

	      dynamic  [offset]	 [lease-time]  --  Automatically  set  the  IP
	      address and netmask by replying to DHCP query messages generated
	      by  the  kernel.	 This mode is probably the "cleanest" solution
	      for setting the TCP/IP properties	since it uses  the  well-known
	      DHCP  protocol.  There are, however, two prerequisites for using
	      this mode: (1) The TCP/IP	properties for the  TAP-Win32  adapter
	      must  be	set  to	 "Obtain an IP address automatically," and (2)
	      OpenVPN needs to claim an	IP address in the subnet  for  use  as
	      the  virtual DHCP	server address.	 By default in --dev tap mode,
	      OpenVPN will take	the normally unused first address in the  sub-
	      net.   For  example,  if	your  subnet  is  netmask, then OpenVPN will take the	IP address
	      to  use  as the virtual DHCP server address.  In --dev tun mode,
	      OpenVPN will cause the DHCP server to masquerade as if  it  were
	      coming  from the remote endpoint.	 The optional offset parameter
	      is an integer which is > -256 and	< 256 and which	defaults to 0.
	      If offset	is positive, the DHCP server will masquerade as	the IP
	      address at network address + offset.  If offset is negative, the
	      DHCP  server  will  masquerade  as  the  IP address at broadcast
	      address +	offset.	 The Windows ipconfig /all command can be used
	      to show what Windows thinks the DHCP server address is.  OpenVPN
	      will "claim" this	address, so make sure to use a	free  address.
	      Having  said  that,  different OpenVPN instantiations, including
	      different	ends of	the same connection, can share the  same  vir-
	      tual DHCP	server address.	 The lease-time	parameter controls the
	      lease time  of  the  DHCP	 assignment  given  to	the  TAP-Win32
	      adapter,	and is denoted in seconds.  Normally a very long lease
	      time is preferred	because	it prevents routes involving the  TAP-
	      Win32  adapter  from  being  lost	when the system	goes to	sleep.
	      The default lease	time is	one year.

	      netsh -- Automatically set the IP	address	and netmask using  the
	      Windows  command-line  "netsh"  command.	This method appears to
	      work correctly on	Windows	XP but not Windows 2000.

	      ipapi -- Automatically set the IP	address	and netmask using  the
	      Windows IP Helper	API.  This approach does not have ideal	seman-
	      tics, though testing has indicated that it works okay  in	 prac-
	      tice.   If  you  use this	option,	it is best to leave the	TCP/IP
	      properties for the TAP-Win32 adapter  in	their  default	state,
	      i.e. "Obtain an IP address automatically."

	      adaptive -- (Default) Try	dynamic	method initially and fail over
	      to netsh if the DHCP negotiation with the	TAP-Win32 adapter does
	      not  succeed  in	20  seconds.  Such failures have been known to
	      occur when certain third-party firewall  packages	 installed  on
	      the  client  machine block the DHCP negotiation used by the TAP-
	      Win32 adapter.  Note that	if the netsh failover occurs, the TAP-
	      Win32  adapter  TCP/IP  properties  will	be  reset from DHCP to
	      static, and this will cause future OpenVPN  startups  using  the
	      adaptive	mode  to  use  netsh  immediately,  rather than	trying
	      dynamic first.  To "unstick" the adaptive	mode from using	netsh,
	      run  OpenVPN at least once using the dynamic mode	to restore the
	      TAP-Win32	adapter	TCP/IP properties to a DHCP configuration.

       --route-method m
	      Which method m to	use for	adding routes on Windows?

	      adaptive (default) -- Try	IP helper API first.  If  that	fails,
	      fall back	to the route.exe shell command.
	      ipapi -- Use IP helper API.
	      exe -- Call the route.exe	shell command.

       --dhcp-option type [parm]
	      Set  extended  TAP-Win32	TCP/IP	properties,  must be used with
	      --ip-win32 dynamic or --ip-win32 adaptive.  This option  can  be
	      used  to	set  additional	 TCP/IP	 properties  on	 the TAP-Win32
	      adapter, and is particularly useful for configuring  an  OpenVPN
	      client to	access a Samba server across the VPN.

	      DOMAIN name -- Set Connection-specific DNS Suffix.

	      DNS addr -- Set primary domain name server address.  Repeat this
	      option to	set secondary DNS server addresses.

	      WINS addr	-- Set	primary	 WINS  server  address	(NetBIOS  over
	      TCP/IP  Name  Server).  Repeat this option to set	secondary WINS
	      server addresses.

	      NBDD addr	-- Set	primary	 NBDD  server  address	(NetBIOS  over
	      TCP/IP  Datagram	Distribution Server) Repeat this option	to set
	      secondary	NBDD server addresses.

	      NTP addr -- Set primary NTP server address (Network Time	Proto-
	      col).  Repeat this option	to set secondary NTP server addresses.

	      NBT type	--  Set	 NetBIOS  over	TCP/IP	Node  type.   Possible
	      options:	1  =  b-node  (broadcasts), 2 =	p-node (point-to-point
	      name queries to a	WINS server), 4	= m-node (broadcast then query
	      name  server),  and  8  =	h-node (query name server, then	broad-

	      NBS scope-id -- Set NetBIOS over TCP/IP Scope. A	NetBIOS	 Scope
	      ID  provides  an	extended  naming  service for the NetBIOS over
	      TCP/IP (Known as NBT) module. The	primary	purpose	of  a  NetBIOS
	      scope  ID	 is  to	isolate	NetBIOS	traffic	on a single network to
	      only those nodes with the	same NetBIOS scope  ID.	  The  NetBIOS
	      scope  ID	 is a character	string that is appended	to the NetBIOS
	      name. The	NetBIOS	scope ID on two	hosts must match, or  the  two
	      hosts will not be	able to	communicate. The NetBIOS Scope ID also
	      allows computers to use the same computer	 name,	as  they  have
	      different	 scope IDs. The	Scope ID becomes a part	of the NetBIOS
	      name, making the name  unique.   (This  description  of  NetBIOS
	      scopes courtesy of

	      DISABLE-NBT -- Disable Netbios-over-TCP/IP.

	      Note that	if --dhcp-option is pushed via --push to a non-windows
	      client, the option will be saved	in  the	 client's  environment
	      before   the   up	  script  is  called,  under  the  name	 "for-

       --tap-sleep n
	      Cause OpenVPN to sleep for n seconds immediately after the  TAP-
	      Win32 adapter state is set to "connected".

	      This option is intended to be used to troubleshoot problems with
	      the --ifconfig and --ip-win32 options, and is used to  give  the
	      TAP-Win32	 adapter  time to come up before Windows IP Helper API
	      operations are applied to	it.

	      Output OpenVPN's view of the system routing  table  and  network
	      adapter list to the syslog or log	file after the TUN/TAP adapter
	      has been brought up and any routes have been added.

	      Block DNS	servers	on  other  network  adapters  to  prevent  DNS
	      leaks.  This  option prevents any	application from accessing TCP
	      or UDP port 53 except one	inside the  tunnel.  It	 uses  Windows
	      Filtering	Platform (WFP) and works on Windows Vista or later.

	      This  option  is considered unknown on non-Windows platforms and
	      unsupported on Windows XP, resulting in fatal  error.   You  may
	      want  to	use --setenv opt or --ignore-unknown-option (not suit-
	      able for Windows XP) to ignore said error.   Note	 that  pushing
	      unknown options from server does not trigger fatal errors.

	      Ask  Windows  to	renew  the TAP adapter lease on	startup.  This
	      option is	normally unnecessary, as Windows  automatically	 trig-
	      gers  a  DHCP renegotiation on the TAP adapter when it comes up,
	      however if you set the TAP-Win32 adapter Media  Status  property
	      to "Always Connected", you may need this flag.

	      Ask  Windows to release the TAP adapter lease on shutdown.  This
	      option has the same caveats as --dhcp-renew above.

	      Run net stop dnscache, net start	dnscache,  ipconfig  /flushdns
	      and  ipconfig  /registerdns  on  connection initiation.  This is
	      known to kick Windows into recognizing pushed DNS	servers.

	      Put up a "press any key to  continue"  message  on  the  console
	      prior  to	 OpenVPN  program  exit.  This option is automatically
	      used by the Windows explorer when	OpenVPN	is run on a configura-
	      tion file	using the right-click explorer menu.

       --service exit-event [0|1]
	      Should  be  used when OpenVPN is being automatically executed by
	      another program in such a	context	that no	interaction  with  the
	      user via display or keyboard is possible.	 In general, end-users
	      should never need	to explicitly use this option, as it is	 auto-
	      matically	 added	by  the	 OpenVPN  service wrapper when a given
	      OpenVPN configuration is being run as a service.

	      exit-event is the	name of	a Windows  global  event  object,  and
	      OpenVPN will continuously	monitor	the state of this event	object
	      and exit when it becomes signaled.

	      The second parameter indicates the initial state	of  exit-event
	      and normally defaults to 0.

	      Multiple	OpenVPN	 processes can be simultaneously executed with
	      the same exit-event parameter.  In  any  case,  the  controlling
	      process  can  signal  exit-event,	 causing all such OpenVPN pro-
	      cesses to	exit.

	      When executing an	OpenVPN	process	using the --service directive,
	      OpenVPN  will  probably not have a console window	to output sta-
	      tus/error	messages, therefore it	is  useful  to	use  --log  or
	      --log-append to write these messages to a	file.

	      (Standalone)  Show  available  TAP-Win32	adapters  which	can be
	      selected using the --dev-node option.  On	 non-Windows  systems,
	      the ifconfig(8) command provides similar functionality.

       --allow-nonadmin	[TAP-adapter]
	      (Standalone)  Set	 TAP-adapter to	allow access from non-adminis-
	      trative accounts.	 If TAP-adapter	is omitted, all	 TAP  adapters
	      on the system will be configured to allow	non-admin access.  The
	      non-admin	access setting will only persist  for  the  length  of
	      time  that the TAP-Win32 device object and driver	remain loaded,
	      and will need to be re-enabled after a reboot, or	if the	driver
	      is unloaded and reloaded.	 This directive	can only be used by an

	      (Standalone) Show	valid subnets for --dev	tun emulation.	 Since
	      the  TAP-Win32  driver exports an	ethernet interface to Windows,
	      and since	TUN devices are	point-to-point in nature, it is	neces-
	      sary  for	 the TAP-Win32 driver to impose	certain	constraints on
	      TUN endpoint address selection.

	      Namely, the point-to-point endpoints used	in TUN	device	emula-
	      tion  must  be the middle	two addresses of a /30 subnet (netmask

	      (Standalone) Show	OpenVPN's view of the system routing table and
	      network adapter list.

   PKCS#11 Standalone Options:
       --show-pkcs11-ids [provider] [cert_private]
	      (Standalone)  Show  PKCS#11 token	object list. Specify cert_pri-
	      vate as 1	if certificates	are stored as private objects.

	      If p11-kit is present on the system, the	provider  argument  is
	      optional;	if omitted the default	module will be

	      --verb option can	be used	BEFORE this option to  produce	debug-
	      ging information.

   IPv6	Related	Options
       The  following  options exist to	support	IPv6 tunneling in peer-to-peer
       and client-server mode.	All options are	modeled	after their IPv4 coun-
       terparts,  so more detailed explanations	given there apply here as well
       (except for --topology ,	which has no effect on IPv6).

       --ifconfig-ipv6 ipv6addr/bits ipv6remote
	      configure	IPv6 address ipv6addr/bits on the ``tun'' device.  The
	      second  parameter	is used	as route target	for --route-ipv6 if no
	      gateway is specified.

       --route-ipv6 ipv6addr/bits [gateway] [metric]
	      setup IPv6 routing in the	system to send the specified IPv6 net-
	      work into	OpenVPN's ``tun'' device

       --server-ipv6 ipv6addr/bits
	      convenience-function  to enable a	number of IPv6 related options
	      at   once,   namely    --ifconfig-ipv6,	 --ifconfig-ipv6-pool,
	      --tun-ipv6  and  --push  tun-ipv6	 Is  only accepted if ``--mode
	      server'' or ``--server'' is set.

       --ifconfig-ipv6-pool ipv6addr/bits
	      Specify an IPv6 address pool for dynamic assignment to  clients.
	      The  pool	 starts	at ipv6addr and	increments by +1 for every new
	      client (linear mode).  The /bits setting controls	 the  size  of
	      the  pool.  Due to implementation	details, the pool size must be
	      between /64 and /112.

       --ifconfig-ipv6-push ipv6addr/bits ipv6remote
	      for ccd/ per-client static  IPv6	interface  configuration,  see
	      --client-config-dir and --ifconfig-push for more details.

       --iroute-ipv6 ipv6addr/bits
	      for   ccd/  per-client  static  IPv6  route  configuration,  see
	      --iroute for more	details	how to setup and  use  this,  and  how
	      --iroute and --route interact.

       OpenVPN	exports	 a  series of environmental variables for use by user-
       defined scripts.

   Script Order	of Execution
       --up   Executed after TCP/UDP socket bind and TUN/TAP open.

	      Executed when we have a still untrusted remote peer.

	      Executed after connection	authentication,	or remote  IP  address

	      Executed	in --mode server mode immediately after	client authen-

	      Executed after  connection  authentication,  either  immediately
	      after,  or  some	number	of  seconds  after  as	defined	by the
	      --route-delay option.

	      Executed right before the	routes are removed.

	      Executed in --mode server	mode on	client instance	shutdown.

       --down Executed after TCP/UDP and TUN/TAP close.

	      Executed in --mode server	mode whenever an IPv4 address/route or
	      MAC address is added to OpenVPN's	internal routing table.

	      Executed	in  --mode server mode on new client connections, when
	      the client is still untrusted.

   String Types	and Remapping
       In certain cases, OpenVPN  will	perform	 remapping  of	characters  in
       strings.	  Essentially,	any  characters	 outside  the set of permitted
       characters for each string type will be converted to underbar ('_').

       Q: Why is string	remapping necessary?

       A: It's an important security feature to	prevent	the  malicious	coding
       of  strings  from  untrusted  sources  to  be  passed  as parameters to
       scripts,	saved in the environment, used as a common name, translated to
       a filename, etc.

       Q: Can string remapping be disabled?

       A: Yes, by using	the --no-name-remapping	option,	however	this should be
       considered an advanced option.

       Here is a brief rundown of OpenVPN's current string types and the  per-
       mitted character	class for each string:

       X509  Names:  Alphanumeric,  underbar  ('_'), dash ('-'), dot ('.'), at
       ('@'), colon (':'), slash ('/'),	 and  equal  ('=').   Alphanumeric  is
       defined	as  a character	which will cause the C library isalnum() func-
       tion to return true.

       Common Names: Alphanumeric, underbar ('_'), dash	('-'), dot ('.'),  and
       at ('@').

       --auth-user-pass	 username:  Same  as  Common Name, with	one exception:
       starting	with OpenVPN 2.0.1,  the  username  is	passed	to  the	 OPEN-
       VPN_PLUGIN_AUTH_USER_PASS_VERIFY	plugin in its raw form,	without	string

       --auth-user-pass	password: Any "printable" character except CR  or  LF.
       Printable  is  defined to be a character	which will cause the C library
       isprint() function to return true.

       --client-config-dir filename as derived from common name	 or  username:
       Alphanumeric,  underbar ('_'), dash ('-'), and dot ('.')	except for "."
       or ".." as standalone strings.  As of 2.0.1-rc6,	the at ('@') character
       has been	added as well for compatibility	with the common	name character

       Environmental variable names: Alphanumeric or underbar ('_').

       Environmental variable values: Any printable character.

       For all cases, characters in a string which  are	 not  members  of  the
       legal character class for that string type will be remapped to underbar

   Environmental Variables
       Once set, a variable is persisted indefinitely until it is reset	 by  a
       new value or a restart,

       As  of  OpenVPN 2.0-beta12, in server mode, environmental variables set
       by OpenVPN are scoped according to the client objects they are  associ-
       ated with, so there should not be any issues with scripts having	access
       to stale, previously set	variables  which  refer	 to  different	client

	      Total  number  of	bytes received from client during VPN session.
	      Set prior	to execution of	the --client-disconnect	script.

	      Total number of bytes sent to client during  VPN	session.   Set
	      prior to execution of the	--client-disconnect script.

	      The  X509	 common	name of	an authenticated client.  Set prior to
	      execution	  of   --client-connect,   --client-disconnect,	   and
	      --auth-user-pass-verify scripts.

       config Name  of	first  --config	 file.	 Set on	program	initiation and
	      reset on SIGHUP.

       daemon Set to "1" if the	--daemon directive is specified, or "0"	other-
	      wise.  Set on program initiation and reset on SIGHUP.

	      Set  to  "1"  if the --log or --log-append directives are	speci-
	      fied, or "0" otherwise.  Set on program initiation and reset  on

       dev    The  actual  name	of the TUN/TAP device, including a unit	number
	      if it exists.  Set prior to --up or --down script	execution.

	      On Windows, the device index of the TUN/TAP adapter (to be  used
	      in  netsh.exe  calls which sometimes just	do not work right with
	      interface	names).	 Set prior to --up or --down script execution.

	      An  option pushed	via --push to a	client which does not natively
	      support it, such as --dhcp-option	on a non-Windows system,  will
	      be  recorded  to	this  environmental variable sequence prior to
	      --up script execution.

	      The broadcast address for	the virtual ethernet segment which  is
	      derived  from the	--ifconfig option when --dev tap is used.  Set
	      prior to OpenVPN calling the ifconfig or netsh (windows  version
	      of ifconfig) commands which normally occurs prior	to --up	script

	      The local	VPN endpoint IPv6 address specified  in	 the  --ifcon-
	      fig-ipv6 option (first parameter).  Set prior to OpenVPN calling
	      the ifconfig or netsh (windows  version  of  ifconfig)  commands
	      which normally occurs prior to --up script execution.

	      The  prefix  length  of  the  IPv6 network on the	VPN interface.
	      Derived from the /nnn parameter  of  the	IPv6  address  in  the
	      --ifconfig-ipv6  option (first parameter).  Set prior to OpenVPN
	      calling the ifconfig or netsh (windows version of	ifconfig) com-
	      mands which normally occurs prior	to --up	script execution.

	      The  remote  VPN endpoint	IPv6 address specified in the --ifcon-
	      fig-ipv6 option (second parameter).  Set prior to	OpenVPN	 call-
	      ing the ifconfig or netsh	(windows version of ifconfig) commands
	      which normally occurs prior to --up script execution.

	      The local	VPN endpoint IP	address	specified  in  the  --ifconfig
	      option  (first  parameter).   Set	 prior	to OpenVPN calling the
	      ifconfig or netsh	(windows version of ifconfig)  commands	 which
	      normally occurs prior to --up script execution.

	      The  remote  VPN endpoint	IP address specified in	the --ifconfig
	      option (second parameter)	when --dev tun is used.	 Set prior  to
	      OpenVPN calling the ifconfig or netsh (windows version of	ifcon-
	      fig) commands which normally occurs prior	to --up	script	execu-

	      The  subnet  mask	of the virtual ethernet	segment	that is	speci-
	      fied as the second parameter to --ifconfig  when	--dev  tap  is
	      being  used.  Set	prior to OpenVPN calling the ifconfig or netsh
	      (windows version of ifconfig)  commands  which  normally	occurs
	      prior to --up script execution.

	      The  local  virtual IP address for the TUN/TAP tunnel taken from
	      an --ifconfig-push directive if specified, or otherwise from the
	      ifconfig	pool  (controlled  by  the --ifconfig-pool config file
	      directive).  Only	set for	--dev tun tunnels.  This option	is set
	      on  the  server  prior  to execution of the --client-connect and
	      --client-disconnect scripts.

	      The virtual IP netmask for the  TUN/TAP  tunnel  taken  from  an
	      --ifconfig-push  directive  if  specified, or otherwise from the
	      ifconfig pool (controlled	by  the	 --ifconfig-pool  config  file
	      directive).  Only	set for	--dev tap tunnels.  This option	is set
	      on the server prior to execution	of  the	 --client-connect  and
	      --client-disconnect scripts.

	      The  remote virtual IP address for the TUN/TAP tunnel taken from
	      an --ifconfig-push directive if specified, or otherwise from the
	      ifconfig	pool  (controlled  by  the --ifconfig-pool config file
	      directive).  This	option is set on the server prior to execution
	      of the --client-connect and --client-disconnect scripts.

	      The  maximum packet size (not including the IP header) of	tunnel
	      data in UDP tunnel transport mode.  Set prior to --up or	--down
	      script execution.

       local  The  --local  parameter.	Set on program initiation and reset on

	      The local	port number, specified by --port or --lport.   Set  on
	      program initiation and reset on SIGHUP.

	      The  password  provided  by  a  connecting client.  Set prior to
	      --auth-user-pass-verify script execution only when  the  via-env
	      modifier	is  specified,	and deleted from the environment after
	      the script returns.

       proto  The --proto parameter.  Set on program initiation	and  reset  on

	      The  --remote parameter.	Set on program initiation and reset on

	      The remote port number, specified	by --port or --rport.  Set  on
	      program initiation and reset on SIGHUP.

	      The pre-existing default IP gateway in the system	routing	table.
	      Set prior	to --up	script execution.

	      The default gateway used by --route  options,  as	 specified  in
	      either  the  --route-gateway  option  or the second parameter to
	      --ifconfig when --dev tun	 is  specified.	  Set  prior  to  --up
	      script execution.

	      A	 set of	variables which	define each route to be	added, and are
	      set prior	to --up	script execution.

	      parm will	be one of "network", "netmask",	 "gateway",  or	 "met-

	      n	is the OpenVPN route number, starting from 1.

	      If  the  network	or  gateway are	resolvable DNS names, their IP
	      address translations will	be recorded rather than	their names as
	      denoted on the command line or configuration file.

	      A	set of variables which define each IPv6	route to be added, and
	      are set prior to --up script execution.

	      parm will	be one of "network" or "gateway"  ("netmask"  is  con-
	      tained  as  "/nnn"  in  the  route_ipv6_network_{n}, unlike IPv4
	      where it is passed in a separate environment variable).

	      n	is the OpenVPN route number, starting from 1.

	      If the network or	gateway	are resolvable	DNS  names,  their  IP
	      address translations will	be recorded rather than	their names as
	      denoted on the command line or configuration file.

	      Temporary	file name containing the client	certificate upon  con-
	      nection.	Useful in conjunction with --tls-verify

	      Set  to  "init"  or "restart" prior to up/down script execution.
	      For more information, see	documentation for --up.

	      Prior to execution of any	script,	this variable is  set  to  the
	      type  of	script being run.  It can be one of the	following: up,
	      down,  ipchange,	route-up,  tls-verify,	auth-user-pass-verify,
	      client-connect,  client-disconnect, or learn-address.  Set prior
	      to execution of any script.

       signal The reason for exit or restart.  Can be one of sigusr1,  sighup,
	      sigterm,	sigint,	 inactive  (controlled	by --inactive option),
	      ping-exit	(controlled by --ping-exit option), ping-restart (con-
	      trolled  by  --ping-restart option), connection-reset (triggered
	      on TCP connection	reset),	error, or  unknown  (unknown  signal).
	      This variable is set just	prior to down script execution.

	      Client  connection timestamp, formatted as a human-readable time
	      string.  Set prior to execution of the --client-connect  script.

	      The  duration  (in  seconds)  of the client session which	is now
	      disconnecting.  Set prior	to execution of	 the  --client-discon-
	      nect script.

	      Client   connection  timestamp,  formatted  as  a	 unix  integer
	      date/time	value.	Set prior to execution of the --client-connect

	      Contains	the  certificate  SHA1	fingerprint/digest hash	value,
	      where n is the verification level.  Only	set  for  TLS  connec-
	      tions.  Set prior	to execution of	--tls-verify script.

	      A	 series	of certificate fields from the remote peer, where n is
	      the verification level.  Only  set  for  TLS  connections.   Set
	      prior to execution of --tls-verify script.

	      The serial number	of the certificate from	the remote peer, where
	      n	is the verification level.  Only set for TLS connections.  Set
	      prior  to	 execution of --tls-verify script. This	is in the form
	      of a decimal string like	"933971680",  which  is	 suitable  for
	      doing  serial-based  OCSP	 queries (with OpenSSL,	do not prepend
	      "0x" to the string) If something goes wrong  while  reading  the
	      value  from  the certificate it will be an empty string, so your
	      code     should	  check	    that.	See	 the	  con-
	      trib/OCSP_check/ script for an example.

	      Like tls_serial_{n}, but in hex form (e.g. "12:34:56:78:9A").

	      The  MTU	of  the	 TUN/TAP  device.  Set prior to	--up or	--down
	      script execution.

       trusted_ip (or trusted_ip6)
	      Actual IP	address	of connecting client or	peer  which  has  been
	      authenticated.	Set   prior   to   execution   of  --ipchange,
	      --client-connect,	and  --client-disconnect  scripts.   If	 using
	      ipv6 endpoints (udp6, tcp6), trusted_ip6 will be set instead.

	      Actual  port  number of connecting client	or peer	which has been
	      authenticated.   Set   prior   to	  execution   of   --ipchange,
	      --client-connect,	and --client-disconnect	scripts.

       untrusted_ip (or	untrusted_ip6)
	      Actual  IP  address  of  connecting client or peer which has not
	      been authenticated yet.  Sometimes used to nmap  the  connecting
	      host  in	a --tls-verify script to ensure	it is firewalled prop-
	      erly.    Set   prior   to	  execution   of   --tls-verify	   and
	      --auth-user-pass-verify scripts.	If using ipv6 endpoints	(udp6,
	      tcp6), untrusted_ip6 will	be set instead.

	      Actual port number of connecting client or peer  which  has  not
	      been  authenticated yet.	Set prior to execution of --tls-verify
	      and --auth-user-pass-verify scripts.

	      The username provided by a  connecting  client.	Set  prior  to
	      --auth-user-pass-verify  script  execution only when the via-env
	      modifier is specified.

	      An X509 subject field from the remote peer certificate, where  n
	      is  the  verification level.  Only set for TLS connections.  Set
	      prior to execution of --tls-verify  script.   This  variable  is
	      similar  to  tls_id_{n} except the component X509	subject	fields
	      are broken out, and no string remapping occurs  on  these	 field
	      values (except for remapping of control characters to "_").  For
	      example, the following variables would be	 set  on  the  OpenVPN
	      server  using  the  sample  client  certificate  in  sample-keys
	      (client.crt).  Note that the verification	level  is  0  for  the
	      client certificate and 1 for the CA certificate.


       OpenVPN	allows including files in the main configuration for the --ca,
       --cert, --dh, --extra-certs, --key, --pkcs12, --secret  and  --tls-auth

       Each  inline  file  started  by the line	<option> and ended by the line

       Here is an example of an	inline file usage

	   -----END CERTIFICATE-----

       When using the inline file feature with --pkcs12	the inline file	has to
       be  base64 encoded. Encoding of a .p12 file into	base64 can be done for
       example with OpenSSL by running openssl base64 -in input.p12

       SIGHUP Cause OpenVPN to close  all  TUN/TAP  and	 network  connections,
	      restart,	re-read	 the  configuration  file (if any), and	reopen
	      TUN/TAP and network connections.

	      Like SIGHUP, except don't	re-read	configuration file, and	possi-
	      bly  don't  close	 and reopen TUN/TAP device, re-read key	files,
	      preserve	local  IP  address/port,  or  preserve	most  recently
	      authenticated  remote  IP	 address/port  based on	--persist-tun,
	      --persist-key,   --persist-local-ip,   and   --persist-remote-ip
	      options respectively (see	above).

	      This signal may also be internally generated by a	timeout	condi-
	      tion, governed by	the --ping-restart option.

	      This signal, when	combined with --persist-remote-ip, may be sent
	      when  the	 underlying parameters of the host's network interface
	      change such as when the host is a	DHCP client and	is assigned  a
	      new IP address.  See --ipchange above for	more information.

	      Causes  OpenVPN to display its current statistics	(to the	syslog
	      file if --daemon is used,	or stdout otherwise).

	      Causes OpenVPN to	exit gracefully.

       If you are running Linux	2.4.7 or higher, you probably have the TUN/TAP
       driver already installed.  If so, there are still a few things you need
       to do:

       Make device: mknod /dev/net/tun c 10 200

       Load driver: modprobe tun

       Prior to	running	these examples,	you should have	OpenVPN	 installed  on
       two  machines  with network connectivity	between	them.  If you have not
       yet installed OpenVPN, consult the INSTALL file included	in the OpenVPN

   TUN/TAP Setup:
       If you are using	Linux 2.4 or higher, make the tun device node and load
       the tun module:

	      mknod /dev/net/tun c 10 200

	      modprobe tun

       If you installed	from RPM, the mknod step may be	omitted,  because  the
       RPM install does	that for you.

       Only Linux 2.4 and newer	are supported.

       For   other   platforms,	 consult  the  INSTALL	file  at  http://open- for	more information.

   Firewall Setup:
       If firewalls exist between the two machines, they should	be set to for-
       ward UDP	port 1194 in both directions.  If you do not have control over
       the firewalls between the two machines, you may still be	 able  to  use
       OpenVPN	by adding --ping 15 to each of the openvpn commands used below
       in the examples (this will cause	each peer to send out a	 UDP  ping  to
       its  remote  peer  once every 15	seconds	which will cause many stateful
       firewalls to forward packets in both  directions	 without  an  explicit
       firewall	rule).

       If you are using	a Linux	iptables-based firewall, you may need to enter
       the following command to	allow incoming packets on the TUN device:

	      iptables -A INPUT	-i tun+	-j ACCEPT

       See the firewalls section below for  more  information  on  configuring
       firewalls for use with OpenVPN.

   VPN Address Setup:
       For  purposes of	our example, our two machines will be called bob.exam- and  If you are constructing a VPN over  the
       internet,  then	replace	and with the
       internet	hostname or IP address that each machine will use  to  contact
       the other over the internet.

       Now  we will choose the tunnel endpoints.  Tunnel endpoints are private
       IP addresses that only have meaning in the context of  the  VPN.	  Each
       machine	will use the tunnel endpoint of	the other machine to access it
       over the	VPN.  In our example, the tunnel endpoint for
       will be	and for,

       Once  the  VPN  is  established,	 you have essentially created a	secure
       alternate path between the two hosts which is addressed	by  using  the
       tunnel endpoints.  You can control which	network	traffic	passes between
       the hosts (a) over the VPN or (b) independently of the VPN, by choosing
       whether	to use (a) the VPN endpoint address or (b) the public internet
       address,	to access the remote host. For example if you are on bob.exam-	and  you  wish to connect to via ssh without
       using the VPN (since ssh	has its	own built-in security) you  would  use
       the  command  ssh  However in	the same scenario, you
       could also use the command telnet to create a  telnet  session
       with	over the VPN, that would use the VPN to	secure
       the session rather than ssh.

       You can use any address you wish	for the	tunnel endpoints but make sure
       that  they  are	private	addresses (such	as those that begin with 10 or
       192.168)	and that they are not part of any existing subnet on the  net-
       works  of  either peer, unless you are bridging.	 If you	use an address
       that is part of your local subnet for either of the  tunnel  endpoints,
       you will	get a weird feedback loop.

   Example 1: A	simple tunnel without security
       On bob:

	      openvpn	--remote   --dev  tun1  --ifconfig	--verb 9

       On alice:

	      openvpn --remote --dev tun1 --ifconfig --verb 9

       Now verify the tunnel is	working	by pinging across the tunnel.

       On bob:


       On alice:


       The  --verb  9  option will produce verbose output, similar to the tcp-
       dump(8) program.	 Omit the --verb 9 option to have OpenVPN run quietly.

   Example  2:	A  tunnel  with	 static-key  security (i.e. using a pre-shared
       First build a static key	on bob.

	      openvpn --genkey --secret	key

       This command will build a random	key file called	key (in	ascii format).
       Now  copy key to	alice over a secure medium such	as by using the	scp(1)

       On bob:

	      openvpn  --remote   --dev   tun1   --ifconfig	--verb 5 --secret key

       On alice:

	      openvpn  --remote	--dev tun1 --ifconfig --verb 5	--secret key

       Now verify the tunnel is	working	by pinging across the tunnel.

       On bob:


       On alice:


   Example 3: A	tunnel with full TLS-based security
       For this	test, we will designate	bob as the TLS client and alice	as the
       TLS  server.   Note  that client	or server designation only has meaning
       for the TLS subsystem. It has no	 bearing  on  OpenVPN's	 peer-to-peer,
       UDP-based communication model.

       First,  build  a	 separate  certificate/key pair	for both bob and alice
       (see above where	--cert is discussed for	more  info).   Then  construct
       Diffie  Hellman	parameters (see	above where --dh is discussed for more
       info).	You  can  also	use  the  included  test   files   client.crt,
       client.key, server.crt, server.key and ca.crt.  The .crt	files are cer-
       tificates/public-keys, the .key files are private keys, and ca.crt is a
       certification  authority	who has	signed both client.crt and server.crt.
       For Diffie Hellman parameters you can use the included file dh1024.pem.
       Note  that  all	client,	server,	and certificate	authority certificates
       and keys	included in the	OpenVPN	distribution are totally insecure  and
       should be used for testing only.

       On bob:

	      openvpn	--remote   --dev  tun1  --ifconfig	--tls-client  --ca  ca.crt  --cert  client.crt
	      --key client.key --reneg-sec 60 --verb 5

       On alice:

	      openvpn  --remote	--dev tun1 --ifconfig	--tls-server  --dh  dh1024.pem	--ca   ca.crt	--cert
	      server.crt --key server.key --reneg-sec 60 --verb	5

       Now verify the tunnel is	working	by pinging across the tunnel.

       On bob:


       On alice:


       Notice  the --reneg-sec 60 option we used above.	 That tells OpenVPN to
       renegotiate the data channel keys every minute.	Since we used --verb 5
       above, you will see status information on each new key negotiation.

       For  production	operations, a key renegotiation	interval of 60 seconds
       is probably too frequent.  Omit the --reneg-sec 60 option to use	 Open-
       VPN's default key renegotiation interval	of one hour.

       Assuming	 you  can  ping	across the tunnel, the next step is to route a
       real subnet over	the secure tunnel.  Suppose that bob  and  alice  have
       two  network  interfaces	 each,	one connected to the internet, and the
       other to	a private network.  Our	goal is	to securely connect both  pri-
       vate networks.  We will assume that bob's private subnet	is
       and alice's is

       First, ensure that IP forwarding	is enabled on both peers.   On	Linux,
       enable routing:

	      echo 1 > /proc/sys/net/ipv4/ip_forward

       and enable TUN packet forwarding	through	the firewall:

	      iptables -A FORWARD -i tun+ -j ACCEPT

       On bob:

	      route add	-net netmask gw

       On alice:

	      route add	-net netmask gw

       Now any machine on the subnet can access any	machine	on the subnet over the secure tunnel (or vice versa).

       In a production environment, you	could put the route  command(s)	 in  a
       script and execute with the --up	option.

       OpenVPN's usage of a single UDP port makes it fairly firewall-friendly.
       You should add an entry to your firewall	rules to allow incoming	 Open-
       VPN packets.  On	Linux 2.4+:

	      iptables -A INPUT	-p udp -s --dport 1194 -j ACCEPT

       This  will  allow  incoming packets on UDP port 1194 (OpenVPN's default
       UDP port) from an OpenVPN peer at

       If you are using	HMAC-based packet authentication (the default  in  any
       of  OpenVPN's  secure  modes),  having  the  firewall  filter on	source
       address can be considered optional, since HMAC packet authentication is
       a  much	more  secure  method of	verifying the authenticity of a	packet
       source.	In that	case:

	      iptables -A INPUT	-p udp --dport 1194 -j ACCEPT

       would be	adequate and would not render the host inflexible with respect
       to its peer having a dynamic IP address.

       OpenVPN	also works well	on stateful firewalls.	In some	cases, you may
       not need	to add any static rules	to the firewall	list if	you are	 using
       a  stateful  firewall  that knows how to	track UDP connections.	If you
       specify --ping n, OpenVPN will be guaranteed to send a  packet  to  its
       peer  at	 least	once  every n seconds.	If n is	less than the stateful
       firewall	connection timeout, you	can  maintain  an  OpenVPN  connection
       indefinitely without explicit firewall rules.

       You  should also	add firewall rules to allow incoming IP	traffic	on TUN
       or TAP devices such as:

	      iptables -A INPUT	-i tun+	-j ACCEPT

       to allow	input packets from tun devices,

	      iptables -A FORWARD -i tun+ -j ACCEPT

       to allow	input packets from tun devices to be forwarded to other	 hosts
       on the local network,

	      iptables -A INPUT	-i tap+	-j ACCEPT

       to allow	input packets from tap devices,	and

	      iptables -A FORWARD -i tap+ -j ACCEPT

       to  allow input packets from tap	devices	to be forwarded	to other hosts
       on the local network.

       These rules are secure if  you  use  packet  authentication,  since  no
       incoming	packets	will arrive on a TUN or	TAP virtual device unless they
       first pass an HMAC authentication test.


       For a more comprehensive	guide to setting up OpenVPN  in	 a  production
       setting,	see the	OpenVPN	HOWTO at

       For  a  description  of OpenVPN's underlying protocol, see http://open-

       OpenVPN's web site is at

       Go here to download the latest version of  OpenVPN,  subscribe  to  the
       mailing lists, read the mailing list archives, or browse	the SVN	repos-

       Report all bugs to the OpenVPN team <>.

       dhcpcd(8), ifconfig(8), openssl(1), route(8), scp(1) ssh(1)

       This product includes software  developed  by  the  OpenSSL  Project  ( )

       For     more	information	on     the     TLS    protocol,	   see

       For more	information on	the  LZO  real-time  compression  library  see

       Copyright (C) 2002-2010 OpenVPN Technologies, Inc. This program is free
       software; you can redistribute it and/or	modify it under	the  terms  of
       the GNU General Public License version 2	as published by	the Free Soft-
       ware Foundation.

       James Yonan <>

			       17 November 2008			    openvpn(8)


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